What Causes Nausea After Intercourse When On Sprintec Birth Control Pills?

Hi I m on sprintec birth control and every time my boyfriend and I have sex he ejactulates inside of me all the time and I always feel nauses and not feel good and my belly been felling weird I feel like I did when I had my first baby. I been on birth control for about 3 months now but my boyfriend and I always have unprotected sex and he doesn t pull out