Sex blues with new bf, advice welcome

We finally had sex and it was everything I hoped it wouldn't be. I gave him a blow job and after a while he grew to a wonderful length that was very exciting, but it was still floppy! He also wanted to have sex in my least favorite position, side by side. I think because it's the only way he could keep it from falling out. He told me he was very dominant in the bedroom and experienced, so I hope this isn't something that happens every time. There was little show of experience or dominance. I've never been with a guy that has these problems and he didn't tell me anything about it. I don't even know how to bring it up, I don't want to hurt him but sex is important to me in a relationship. Is this a normal thing that happens to some guys? I'm afraid to ask, if it's a medication for an antidepressant causing it or something I don't want to make him feel bad about it. He seemed aware it was going to happen, like he's used to it. If it keeps happening I don't know what I'm going to do, I'd like to enjoy sex with him to the fullest and show his vanilla self what a freaking decked out banana split sex life can be. Our relationship is so wonderful, I really want the sex to be good too. Any related advice would be appreciated