iphone & app problems!!?

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when i go on my iphone 4s and open an app, such as instagram and facebook after about a minute if that, my phone goes into spazm. It wont slide properly, if i go to type a text and try to write a word such as 'like' the 'i' and the 'k' wont work, its like there is a block from me tapping that part of the screen. I also have trouble getting into my phone, the slider to open it wont slide all the way across it stops half way goes back and bounces and trys to open the camera, which then once i get it across when i type in my password, if i press '9' the number '5' is pressed and if i press '0' cancel gets pressed.
I cant seem to find a solution anywhere!! i've tried to clean my screen that didnt help, i deleted and re installed instagram that didnt help! does anyone have any suggestions?! preferably i would rather not take it to a shop im hoping its a simple thing!
thanks for any help xxx
how do i do a back up? never done it before to deffo make sure none of my files or anything are lost forever?! thanks x