Samsung Galaxy S II :: Constant Force Closes And Loss Of Stored Data?

I've had my phone since April and has recently started to experience a lot of problems with the handset. I'm best mentioning that my technical know-how is very limited in terms of phones, but I've accepted the fact I'm going to have to run a factory reset on my phone. So the problems I'm experiencing:- All of a sudden, apps start crashing one after the other. So much so that I can't even turn the phone off properly and just have to hold the power button down until it goes off itself.- Sometimes it just freezes, and when it does, it rapidly drains the battery.- Other times it just randomly decides to turn itself off (this has happened during the night resulting in me sleeping in for work because my alarm has failed to go off!)- When apps have crashed and I've had to turn it on and off again, all information stored (ie. texts, photos, Twitter feed) after the 16th October is gone!I've even went on Kies Air to start transferring photos, videos, etc. to my laptop, but even that keeps crashing, meaning it constantly disconnects from the laptop. I cleared out a lot of old apps I don't use anymore, but they reappear when I turn it back on, resetting back to pre-16th October like I mentioned.