I've got a similar problem, my memory may be the reason as it is only 4GB. I've had Yosemite for a while now and my macbooks performance has been getting slower and slower. I've downloaded etrecheck and got the following;
EtreCheck version: 2.1.8 (121)
Report generated 11 March 2015 16:51:22 GMT
Download EtreCheck from http://etresoft.com/etrecheck
Click the [Click for support] links for help with non-Apple products.
Click the [Click for details] links for more information about that line.
Click the [Adware! - Remove] links for help removing adware.
Hardware Information: ℹ️
MacBook Pro (13-inch, Mid 2012) (Technical Specifications)
MacBook Pro - model: MacBookPro9,2
1 2.5 GHz Intel Core i5 CPU: 2-core
4 GB RAM Upgradeable
BANK 0/DIMM0
2 GB DDR3 1600 MHz ok
BANK 1/DIMM0
2 GB DDR3 1600 MHz ok
Bluetooth: Good - Handoff/Airdrop2 supported
Wireless: en1: 802.11 a/b/g/n
Battery Health: Normal - Cycle count 380
Video Information: ℹ️
Intel HD Graphics 4000
Color LCD 1280 x 800
System Software: ℹ️
OS X 10.10.2 (14C109) - Time since boot: 6 days 4:5:10
Disk Information: ℹ️
APPLE HDD ST500LM012 disk0 : (500.11 GB)
EFI (disk0s1) <not mounted> : 210 MB
Recovery HD (disk0s3) <not mounted> [Recovery]: 650 MB
Macintosh HD (disk1) / : 498.88 GB (232.66 GB free)
Encrypted AES-XTS Unlocked
Core Storage: disk0s2 499.25 GB Online
MATSHITADVD-R UJ-8A8
USB Information: ℹ️
Apple Inc. FaceTime HD Camera (Built-in)
Apple Computer, Inc. IR Receiver
Apple Inc. BRCM20702 Hub
Apple Inc. Bluetooth USB Host Controller
Apple Inc. Apple Internal Keyboard / Trackpad
Thunderbolt Information: ℹ️
Apple Inc. thunderbolt_bus
Gatekeeper: ℹ️
Anywhere
Adware: ℹ️
Geneio [Adware! - Remove]
Downlite [Adware! - Remove]
Kernel Extensions: ℹ️
/Applications/spotflux.app
[not loaded] com.spotflux.Spotflux.tap (1.0) [Click for support]
[loaded] com.spotflux.Spotflux.tun (1.0) [Click for support]
/Library/Application Support/Avast/components/fileshield/unsigned
[loaded] com.avast.AvastFileShield (2.1.0 - SDK 10.9) [Click for support]
/Library/Application Support/Avast/components/proxy/unsigned
[loaded] com.avast.PacketForwarder (2.0 - SDK 10.9) [Click for support]
/System/Library/Extensions
[not loaded] com.devguru.driver.SamsungComposite (1.4.20 - SDK 10.6) [Click for support]
/System/Library/Extensions/ssuddrv.kext/Contents/PlugIns
[not loaded] com.devguru.driver.SamsungACMControl (1.4.20 - SDK 10.6) [Click for support]
[not loaded] com.devguru.driver.SamsungACMData (1.4.20 - SDK 10.6) [Click for support]
[not loaded] com.devguru.driver.SamsungMTP (1.4.20 - SDK 10.5) [Click for support]
[not loaded] com.devguru.driver.SamsungSerial (1.4.20 - SDK 10.6) [Click for support]
Problem System Launch Agents: ℹ️
[killed] com.apple.bird.plist
[killed] com.apple.CallHistoryPluginHelper.plist
[killed] com.apple.CallHistorySyncHelper.plist
[killed] com.apple.cloudd.plist
[killed] com.apple.cmfsyncagent.plist
[killed] com.apple.coreservices.appleid.authentication.plist
[killed] com.apple.Maps.pushdaemon.plist
[killed] com.apple.nsurlsessiond.plist
[killed] com.apple.pluginkit.pkd.plist
[killed] com.apple.rcd.plist
[killed] com.apple.recentsd.plist
[killed] com.apple.scopedbookmarkagent.xpc.plist
[killed] com.apple.security.cloudkeychainproxy.plist
[killed] com.apple.telephonyutilities.callservicesd.plist
14 processes killed due to memory pressure
Problem System Launch Daemons: ℹ️
[killed] com.apple.AssetCacheLocatorService.plist
[killed] com.apple.awdd.plist
[killed] com.apple.ctkd.plist
[killed] com.apple.emond.aslmanager.plist
[killed] com.apple.GSSCred.plist
[killed] com.apple.icloud.findmydeviced.plist
[killed] com.apple.ifdreader.plist
[killed] com.apple.nehelper.plist
[killed] com.apple.nsurlsessiond.plist
[killed] com.apple.periodic-daily.plist
[killed] com.apple.periodic-weekly.plist
[killed] com.apple.softwareupdate_download_service.plist
[killed] com.apple.systemstats.analysis.plist
[killed] com.apple.wdhelper.plist
[killed] com.apple.xpc.smd.plist
15 processes killed due to memory pressure
Launch Agents: ℹ️
[running] com.avast.update-agent.plist [Click for support]
[loaded] com.avast.userinit.plist [Click for support]
[loaded] com.google.keystone.agent.plist [Click for support]
[failed] com.vsearch.agent.plist [Adware! - Remove]
Launch Daemons: ℹ️
[loaded] com.adobe.fpsaud.plist [Click for support]
[loaded] com.avast.init.plist [Click for support]
[loaded] com.avast.uninstall.plist [Click for support]
[not loaded] com.avast.update.plist [Click for support]
[loaded] com.google.keystone.daemon.plist [Click for support]
[loaded] com.macpaw.CleanMyMac2.Agent.plist [Click for support]
[loaded] com.microsoft.office.licensing.helper.plist [Click for support]
[loaded] com.spotflux.Spotflux.tun.plist [Click for support]
[not loaded] com.vsearch.daemon.plist [Adware! - Remove]
[failed] com.vsearch.helper.plist [Adware! - Remove]
User Launch Agents: ℹ️
[loaded] com.adobe.ARM.[...].plist [Click for support]
[not loaded] com.avast.home.userinit.plist [Click for support]
[failed] com.spotify.webhelper.plist [Click for support]
[loaded] com.valvesoftware.steamclean.plist [Click for support]
User Login Items: ℹ️
Webshots Wallpaper & Screensaver UNKNOWN (missing value)
iTunesHelper Application (/Applications/iTunes.app/Contents/MacOS/iTunesHelper.app)
CrossOver CD Helper Application (/Users/[redacted]/Applications/CrossOver.app/Contents/Resources/CrossOver CD Helper.app)
Dropbox Application (/Applications/Dropbox.app)
Genieo UNKNOWN (missing value)
EvernoteHelper Application (/Applications/Evernote.app/Contents/Library/LoginItems/EvernoteHelper.app)
KiesAgent Application Hidden (/Applications/Kies.app/Contents/MacOS/KiesAgent.app)
fuspredownloader Application Hidden (/Users/[redacted]/Library/Application Support/.FUS/fuspredownloader.app)
Internet Plug-ins: ℹ️
FlashPlayer-10.6: Version: 16.0.0.305 - SDK 10.6 [Click for support]
Default Browser: Version: 600 - SDK 10.10
AdobePDFViewerNPAPI: Version: 11.0.10 - SDK 10.6 [Click for support]
AdobePDFViewer: Version: 11.0.10 - SDK 10.6 [Click for support]
Flash Player: Version: 16.0.0.305 - SDK 10.6 [Click for support]
o1dbrowserplugin: Version: 5.40.2.0 - SDK 10.8 [Click for support]
QuickTime Plugin: Version: 7.7.3
SharePointBrowserPlugin: Version: 14.0.0 [Click for support]
googletalkbrowserplugin: Version: 5.40.2.0 - SDK 10.8 [Click for support]
Silverlight: Version: 5.1.20513.0 - SDK 10.6 [Click for support]
JavaAppletPlugin: Version: 15.0.0 - SDK 10.10 Check version
Safari Extensions: ℹ️
AdBlock
avast! Online Security
3rd Party Preference Panes: ℹ️
Flash Player [Click for support]
Time Machine: ℹ️
Time Machine not configured!
Top Processes by CPU: ℹ️
13% Google Chrome
9% WindowServer
2% hidd
0% systemstatsd
0% SystemUIServer
Top Processes by Memory: ℹ️
125 MB Google Chrome
69 MB Microsoft Word
62 MB Google Chrome Helper
52 MB Finder
47 MB mds_stores
Virtual Memory Information: ℹ️
112 MB Free RAM
1.19 GB Active RAM
1.09 GB Inactive RAM
856 MB Wired RAM
75.98 GB Page-ins
2.45 GB Page-outs
Diagnostics Information: ℹ️
Mar 11, 2015, 04:15:58 PM /Users/[redacted]/Library/Logs/DiagnosticReports/NotificationCenter_2015-03-11- 161558_[redacted].crash
Mar 9, 2015, 10:48:14 PM /Library/Logs/DiagnosticReports/Microsoft Word_2015-03-09-224814_[redacted].cpu_resource.diag [Click for details]
Mar 9, 2015, 09:02:01 PM /Library/Logs/DiagnosticReports/CrossOver_2015-03-09-210201_[redacted].hang
Mar 9, 2015, 11:44:27 AM /Library/Logs/DiagnosticReports/discoveryd_2015-03-09-114427_[redacted].crash