Touch screen unresponsive I phone 5

my girlfriend had a cracked screen so i ordered a new one and replaced it with no problems and everything seemed to be working fine untill she started scrolling through her facebook pages, the screen seemed to stop scrolling suddenly and then not respond for a split second.

I then went to see what its like writing msg's etc and it would write a few letters in sequence and then freeze for a second or two then either respond or write its own choice of letters and do its own thing.

Could this be an issue with the new screen or a possible error on my part of the fitting? Many thanks for any help you can give.