Deep pain during intercourse. Is he just too big for me?

Probably not. This is called "deep dysparunia" and can be associated with pelvic muscle and floor dysfunction. This can sometimes be associated with trauma, short leg syndrome, mva and other issues. It could also be a chronic infection. You should start by seing your doctor for a thorough gynecological exam to evaluate for these other possibilities. If this is negative, consider osteopathic manipulation.