pregnancy and masturbation

so I'm almost 18 weeks and I masturbate probably 2-3 sometimes 4 times a week on top of sexual activity with my baby's father but today after orgasim I felt this slight pressure and felt my stomach tighten and my left side raised up this has never happened in my 18 weeks of pregnancy idk if it was the baby reacting or my body reacting to the orgasim in a way it hasn't before. has anybody else experienced this? I have a doctor appointment tmrw of course I'll be talking to my doctor but thought I'd getting some real life advice from you ladies