I don't know who to ask about this

I am now 25 weeks pregnant and every time my fiancé and I have sex without a condom I have a burning/ hurting feeling all around my vulva. This has never happened before I was pregnant and I didn't start noticing it until two weeks ago. There isn't a problem with lubrication... We've tried condoms and after using condoms I don't have any pain at all. What could be causing this?? (The pain/ itching/ burning lasts for about two days)