What does it mean to have UTI symptoms and treatment for a UTI, but my culture is always negative?

Any nurses or doctors or anyone can explain? I have frequent UTI’s or what I guess I think is a UTI, but my culture is negative always.

Just got off the phone with my Dr. and she told me since they are negative that means something else is going on with my Vagina and that I need a Vaginal Exam . So I’m scheduling one but I’m worried now. What could it possibly be?

Never had yeast infections or BV. Just UTI’s or what I think is a UTI and ONLY after sex.

We shower before, after, and I pee right after. I don’t hold it, I don’t douche, I don’t use perfume or anything to hide any “ scents”.

When I have my UTi’s is just burning when I pee, it smells weird, I keep peeing when nothing comes out, and I need antibiotics for it to go away.

I’ve been with the same partner ( my husband) for 5 years . We were each others firsts and I’ve been on birth control for 3 years. This didn’t start happening until we got married and I moved in with him and we started having sex every week instead of months apart due to distance. (Military).

I am 23 years old, and had my first pap smear last year which came out normal.