What Can Cause Smelly Yellowish Discharge Before Periods?

Hello, I have been having sex more often with my partner in the last 6 months, I've noticed that I had a slight odor and discharge. I went to get a pap smear last month and it came back negative..but now, my discharge is yellowish or greyish-white in color, has a sort of fishy/urine smell at times..I've purchased the BV treatment t kit last week but it seems that the smell has returned after the treatment, and it seems to get stronger during intercourse and right before my period..I'm 41 years old and I take a daily multi-vitamin supplement. Do you know what may be causing this??