How do I prevent body odor?

I always shave every shower and I also us deodorant. But still after a long and hot day in school I can smell myself. I ask my friend if I smell bad she tells me no but still I can smell myself. Not the way a BO usually smells, but it's like perspiration that stick to my skin and it smells awful. I don't smell it often, only when I go to the bathroom and smell my armpit. But I don't know if my clmates smells it too. Please help me I'm already a teenager and I don't want to be smelly. thanks a lot