It could be from your discharge because of your pregnancy, but when it itch and turns reddish, go to your doctor they will give you some medications which is safe for pregnancy. It could be a sign of Urinary Tract Infection which is sometimes happened to pregnant women. You will find it out once they will do some test on you. It happened to me before and it was UTI. Hope this helps.
Yeast infection most likely. DO you have a bad odor at all??