My iPhone 4S screen doesn't respond?

I have an iPhone 4S. I've had a problem where the screen doesn't sense my touch, holds the action if I tap, is very laggy, and the screen flickers sometimes. I've had these problems for about a year now but now it's more consistent and reseting it doesn't seem to fix the problems anymore. I might have to reset it 4-5 times before working for a while. I've tried shutting it off for some time, charging it differently, I deleted like 2GB of space to see if it was that that was making it slow, I connected it to iTunes (that made it work better but the problems persist), I updated all of the apps, etc. I think I've tried everything. Is there a reason for this? Does anyone know what else I could try? It's like the phone has a mind of its own and only works when it wants to.

Does it still hold a charge well. Possibly a weak battery can cause issues. But to get a definite answer, take it to an Apple store and see what they can tell you.