Mac suddenly started being slow, crashing, and glitchy? Help please

Ok,

So I have an eary 2011 model Macbook Pro 13' with 4gb hardrive with a 2.3ghz i5

My mac used to work great, literally no problems, i only do simple stuff like microsoft word, youtube, browse the web, itunes and spotify etc.

Basically the other day i was ordering concert tickets from ticketmaster.com and suddenly my computer like just froze and nothing worked at all so i just held the power button down and let it reboot, then it got so glitchy

it was crashing, nothing was loading, every action i made required the rainbow spinning wheel thing. oh and for some reason the sound option no longer appeard it was like a faded gray, and no sound came from the computer. so i went to the app store and updated my software ( i was on mountain lion but i dont know which version)

since ive updated im on 10.8.4 and that fixed the sound problem, but my computer is still messed up or something

when i boot it up and have to enter in my password it just starts lagging and freezing, everything i do i get the rainbow spinning wheel, spotify fades in and out and constantly freezes as does itunes and safari crashes alot especially when im just trying to play a video. not to mention netflix doesnt play anymore (it keeps saying the plugin failed or something).

i thought it might be a virus but i scanned (with iAntivirus from the mac app store) and it said it was clean. Also my computer takes forever to connect to wifi, before this happened i could open up my computer and it would immediatly connect but now it takes like 3 minutes ( i know that sounds like a petty problem but its an issue when im a student and have to open up my computer and immediatly start working)

ive also checked my activity moniter but nothing shows up as draining the CPU. my ram says its realitivly free

i havent downloaded anything new, i havent dropped my computer or anything either

and just to be clear, my computer had no problems prior to this ticketmaster thing.

thank you in advanced for anyone that can help,

i start school very soon and i really need my computer to work, i rely on it heavily