Why gain fat when exercising so much?

go to gym, 3/4 times a week, cardio and weights mixed, taking supplements also ( zma- bolic support, and nitric oxide - muscle pumps) noticed over the last month or so ive been putting weight on in stomach area. could it be taking the supplements? is it wrong to take both? my diet is good, strict. is it just my age! also take a whey protein shake after work outs. please help!