What can I do if sex makes me sick during pregnancy?

Take a break. Sometimes during pregnancy sex just doesn't feel good. Don't feel pressured to do everything you did before. Fatigue, nausea, hormones can all affect how we feel about sex. And during pregnancy, your body is changing so much, it is hard to keep up. Try new positions or timing. But if sex makes you feel poorly, take a break for a while.
Abstain till Ob seen. It is probably not wise to have sex if it makes you sick. I would see your obstetrician to be sure you are okay.