Do not use Prometrium without your doctor's consent if you are pregnant. Tell your doctor if you become pregnant during treatment. Talk to your doctor about using birth control while you are using Prometrium. Prometrium passes into breast milk and may harm a nursing baby. Consult your doctor before breastfeeding. That doesn't mean the symptoms aren't pregnant related but progesterone does make you feel that way Brianna- Mommy to DS, Brayden Chase 09/01/06 TTC 2 4 I was on prometrium with my last pregnancy, and although the pregnancy didn't work out, it had nothing to do with prometrium. There are so many women on here who took it during pregnancy to have all turn out just fine. Progesterone helps you achieve and maintain pregnancy. During the second half of your menstrual cycle, your progesterone levels go up. The hormone helps thicken the lining of your uterus. If your body no longer makes enough or any progesterone, you can take Prometrium to replace it. Your doctor might prescribe Prometrium if your periods have stopped for several months ( amenorrhea ). I am pregnant again and my doctor put me back on the progesterone suppositories. (They are vaginal suppositories), and so far so good. My doctor also said that progesterone will make you sleepy, but other than that I feel ok. When I was on the other stuff, I didn't feel very well, but I don't know if it was due to the promentrium or not. I am on prometrium also.currently 5 weeks pregnant.i started it a few days after BD and boy do i need it.my first levels on 200mg were 5 and i was pregnant. My side effects started after taking the Prometrium, but my Dr only told me to take them before bed because they make you tired. She never told me about all the other side effects. I've thought I might be pregnant for 2 weeks now and finally read these side effects and realized it is just that-the stupid medication. I'm not going to take them next month because they messed my body up so much. Little things like uploading a profile picture make the community a better place. Thanks! Doctors give trusted answers on uses, effects, side-effects, and cautions: Dr. GalatzerLevy on why does prometrium make you tired: If anything it can make you feel more energetic. Search Sign up free.