Orgasms trigger uterine contractions. Your uterus is stretching for baby 2 and your internal scarring too. If you have any internal keloid or adhesions and your uterus contracting, that’s gonna pull and hurt
Could be pelvic floor pain. Around my incision and down into pubic bone and thighs gets really sore very easily from pelvic floor stuff this pregnancy. I've been told with having a c section and then being pregnant the pelvic floor can stretch a lot and become irritated. I'm 31 weeks pregnant.
Maybe just see a doctor anyway