burning!!

Im 21 weeks & Ive been burning so bad down there especially after sex. It stays for a few days then somewhat goes away until i have sex again or maybe hold my pee in for too long. The Dr prescribed me yeast infection medicine & it didnt help. So he ran some test and he cant find anything wrong but he prescribed me somewhat for bacterial vaginitis just in case. That medicine isnt helping either. This has been happening for the past 3 months. Anybody else??