I am 30 years old (almost 31) and the only time I have orgasmed is with foreplay.. during foreplay.. the touching, learning about each other and teasing.. great build up to the actual act.
i have had a few boyfriends and to be honest the first one I had from 16 - 22 was the BEST when it came to sex. He was 'small' but it's the size that matters I have found... bigger can be a bit frightening and make me tense up LOL.
My first and i tried everything that we could think of, read about or seen (yes we did watch porn together).
You say you don't think it feels good when you are on top.... TALK about it... ask the question, "hey, does that feel good for you?"...
You will probably find that if he says "yes" you will feel more confident in what you are doing and will enjoy everything more.
Talking about sex can be a turn on in it's self, it's all part of learning!