The MacBook Pro model you've stated can be upgraded to more RAM
as indicated by information from http://mactracker.ca database, here:
Maximum Memory 8.0 GB
Memory Slots 2 - 204-pin PC3-8500 (1066 MHz) DDR3 SO-DIMM
•MacBook Pro: How to remove or install memory - Apple Support
If the above matches this other information then you should have no
trouble acquiring quality RAM from vendors such as Crucial.com or
macsales.com (OWC) and be sure to avoid bargain-based RAM as
those kinds of low-end products are less stable & can fail under load.
http://eshop.macsales.com/shop/memory/Apple_MacBook_MacBook_Pro/Upgrade/DDR3
•Information for MacBook Pro (13-inch, Mid 2009) -- to compare specs:
Introduced June 2009
Discontinued April 2010
Model Identifier MacBookPro5,5
Model Number A1278
EMC 2326
Order Number MB990LL/A (2.26 GHz), MB991LL/A (2.53 GHz)
The upgrade of memory chips (RAM) of the correct specification & of
quality reputable brand, is not too difficult; note your MB/Pro in Link.
You may be able to upgrade the internal hard disk drive to greater
capacity, note there is a helpful link to iFixit repair guides; however
it would be best to use a second computer whilst upgrading the first
or have someone who is familiar with the specific model you have
on a technical basis. A different kind of upgrade may include an SSD.
video upgrade guides - OWC macsales:
http://eshop.macsales.com/installvideos/
MacBook Pro 13-inch repair guides - iFixit:
https://www.ifixit.com/Device/MacBook_Pro_13%22
Hopefully you can resolve this issue, however you may need to contact
an Apple Genius at official Apple Store (set appointment ahead of visit)
or a specialist AASP authorized service expert, if you need tech help.
Some independent sales/service providers may specialize in older Macs
and could provide upgrade service on old models no longer seen by an
official Apple Store. The independent shops may do upgrades, etc.
There are some upgrades you or a capable friend, could do yourself.
A genius/specialist could help by inspection/testing, and may suggest
ways of making it work better. As it is getting older, could be a new HDD
& some RAM, may be sufficient and less costly than a new MacBook.
In any event...
Good luck & happy computing! 🙂