Apps on my iphone 4 keep closing?

When I go to a app, lets say facebook (cause this one does it the most), it will come on for a few seconds with the blank screen, close- go back to homepage), and i will click again and then it will take a long time then come on.

Also when i'm on an app for long, e.g. Facebook again, it will pause after i hve pressed send, for about a minute, then close.(but sometime i will close it cause it take too long.

What's going on? Has anyone had this problem?

I know the phone is old but its in really goo condition and i have hardly got any apps on it and has alot of free space.

At the end of august this year i'm gonna get the iphone5 (or 5s if its out then). Hope i will bot have this problem:/

I think you would need a new phone, but if you want to try to fix it somehow here's how.
1. Back up via iTunes and reset your iPhone to factory settings.
2. Reset iPhone. (holding the top and home buttons for 10 seconds)
3. Unlock your iPhone, double click your home button and the bottom row of your screen should come up. Hold down one of your apps and in a few seconds the row should be vibrating, and there should be a little red dot with a line across it. This is stopping the applications you're using so it restarts. Tap every red dot next to the app. Your apps should be refreshed and restarted.

EDIT: Here's how you do #3 if it's not clear: (Skip to 0:22 unless you wanna hear boring stuff.)

It's your phone mine kept doing that was almost out of gigs upgraded with more memory and no problem

My phone does the same with one particular app. But I don't have a SD card so that might be the problem

My phone does the same with one particular app. But I don't have a SD card so that might be the problem