Pregnancy is full of all kinds of different symptoms. Some cause problems, others are annoying and others are embarrassing and look worse than they actually are.
During pregnancy, you can start breaking out in hormonal acne just like you did as a teen, you develop stretch marks and sometimes even random rashes.
Pruritic urticarial papules and plaques of pregnancy or "PUPPP" is an annoying but safe rash that comes during one in 150 pregnancies, roughly. It typically starts in the third trimester and ends in the first few weeks to months postpartum.
The cause is not completely understood. It is known not to be hormonal but there are theories that it could be related to the dad's side of the family (the pregnant woman's dad) or the fetus.
There are some risk factors that have been found, though. If you're a white woman pregnant for the first time with a little boy it is more likely to happen. If you have high blood pressure, are carrying more than one or have gained weight faster than typical those are the other risk factors.
PUPPP usually starts in the stretch marks in the stomach and moves to the butt, hips, thighs and other areas in the next couple of days, but it typically stays below your chest. It looks like small pink pimples or hives. It gets to be very itchy, especially at night.
The only way to really treat it is to treat the itch and wait the rash out. The only "cure" is having the baby but taking a (not too hot) bath in oatmeal helps (make sure it's not a hot bath and not too often since there are risks with baths), using a moisturizer to help the itch also helps. Two treatments you need to talk to your doctor about are using an anti-itch cream (hydrocortisone 1% is said to be potentially safe, but you do need to talk to your OB first) and taking an antihistamine, but once again, speak with your OB first to make sure the medication is safe.
You should always talk to your OB about a rash before starting a home treatment. They have ways of finding out if it's PUPPP and there are other rashes related to pregnancy but some that aren't and you need to make sure it's not something that could be harmful.