Hi, I've Been Sexually Active With My Boyfriend For About

Hi, I've been sexually active with my boyfriend for about 4-5 months now. (We were both virgins) anyways the last like 1-2 months I've been experiencing a burning sensation during sex. I didn't have a yeast infection during these times. I've been we'll lubricated but that doesn't seem to matter. We don't use condoms. I'm not on birth control. Can you please help me figure out what's going on?? -sex distressed