What could it be?

I was having symptoms of a UTI about 3 weeks ago. I've been urinating frequently and have been having the 'burning' feeling off and on. I tried to clear it up on my own because I have no health ins, but that didn't work, so I went to a walk in a week ago. They put me on bactrim, did a culture and sent me home. I called this morning to get the results of the culture and they said it wasn't a UTI and I need to find an OBGYN and have them figure it out. I'm now done with the Bactrim and still having symptoms. They said its not an infection, what else could it be? This doesn't sound like preg. symptoms, right? (please don't respond with dumb obvious answers, yes I am making a dr's appt. I'm just looking for advice from people who have shared a similar experience)What could it be?
It could be a yeast infection.
have you tried drinkin alot of water it always helps trust me!!
It could either be a serious UTI or, more likely, an STD like chlamydia. Either way, you should head to a doctor pronto.