My touch screen occasionally stops working?

I dropped my phone the other day and shattered the screen, so I went to a local store that fixes them and got it repaired. Every thing was absolutely fine until about 24 hours after. My screen will stop responding to touch for a couple of minutes, then act fine, until it has another fit and stops working. I've had them replace the screen before (I'm very clumsy) and the last time they did fine, the only thing that i noticed was that every now and then it would go through fits where it would hit buttons i didnt press but these are rare. Why does my touch screen not respond for only a little while, then it is fine, then it stops working again, then fine etc.?? Thank you in advance