Why am I so jealous. It's starting to affect my marriage!?

I'm 19 years old & I have been with my husband for 2 years. We have been married for 1 year. And I get so easily jealous. If we are watching a movie and there is nudity in it I ask him "Do you think she is sexy or beautiful?" And he says "no I could care less." And he tells me I'm sexy and beautiful & he does everything in his power to make me think that, but I just don't think I am. It's not that I don't believe him. I just don't personally think I'm beautiful or sexy, & I think that's why I get jealous! What can I do to make this kind of stuff stop. I don't want to jealous. He is a good man. I know he doesn't look at other women, but I ask him if he does. And I know he doesn't. Please give advice!!