Look. Find a guy that won't pressure you about stuff like that. You could always try and talk to them about it...say something along the lines of: "I don't want to talk about sex. Not now. I'm too young right now...so can you stop?" Try and focus on other things in your relationships, but if a guy gets too pushy, I would suggest a break up.
Look Its obious that he doesen't care about your feelings. he only wants to satisfy his sexual desires. Dont do do what he asks you if you dont want to. this will come naturally you dont need to force anything. Dump him i know its hard but you won't regret it. Soon you will find a guy who can truly value you.. :) goodluck..