Pain and sex?

I’m 12 weeks pregnant and sometimes during sex I get a pain on the left side of my pelvis/womb area and he doesn’t even have to go too deep for me to feel it. Today we had sex and it started fine but as it went on I started to feel this pain and every time he pushed inside I felt the pain and we eventually had to stop. Should I be worried about this and should I mention it at my first ultrasound next week?