Pain during sex?!

So I'm not a virgin and, ironically my first time didn't hurt. But I have experienced trauma and have PTSD because of it. Finally my current boyfriend and I were ready to try having sex. I thought maybe I was tensing up too much because we had trouble with penetration, including some pain, and eventually gave up. I was also thinking maybe he's just bigger than the other guy I had been with years ago and I' need to...adjust I guess. Anyone had experience with this? (Also I've been to the gyno and she said there wasn't any damage or anything caused by the traumatic experience)