Bleeding during sex?

My boyfriend is 6’2 with a thick 8 incher (we are 17). In past relationships I have never had the problem of bleeding during sex but for some reason every time we go to do it I bleed. Is it because of his size? Is it because I have not had sex in awhile? Ladies please help me!

(The bleeding only lasts 5 minutes and then stops but it’s so embarrassing and he takes it easy on me at first)