home button does not like to work all the time

the home button sometimes works but it does not like to like when i press it once the back round app screen pops up. and it also when i press it once it does not work at all and also when i try to wake it up with the home button it takes around 7 pushes to wake it up ant sometimes it works right away I am so con fused and its been doing this scince i got it and i have had it apart to change the screen but im not sure if that has anything to do with it.