So i started the campaign on easy and then decided a chapter in that i wanted to play hard instead. once i beat the game i had played most of the chapters on hard and then went back and beat the others that i hadn't already done on hard but it wont give me the trophy. even though all the chapters say they were beaten on hard. anyone had this problem?

you have to start a new game on hard. You keep all your stuff, but you loose the chapter selection. 
 
So you could say than instead of a glitch, its a design flaw.

well that sucks ugh i played all of that again on hard for nothing

sweet thanks alot fresh :-)