Was he always this way? Did you feel at all like this before you married him? Were there signs you ignored, hoping or expecting that all would change after you got married? What's you relationship like outside of the bedroom? Are you willing to be creative, daring during sex, or do you have certain hangups that keep you from being free during sex? Is he physically in good shape? Most importantly, how does the communication about this subject go? Does it stop after he declares he's too tired, without explanation? Is he open to going to couples therapy with you to look into this issue further if you cannot talk productively about it? You ARE too young to have to accept this kind of marriage, but there may be a reason for it that has a solution that you haven't discovered yet. Good luck to you!