I had the same issue and my doctor checks my urine every time I go in. She said that commonly during pregnancy you can have vaginal irritation. It doesn't mean you have a uti or anything like that. It could very well be just irritation from the bacteria you already have.
I'll be 28 weeks tomorrow, I've had painful sex the whole time, plus burning after. my doctor said it's caused by the vagina walls drying out, doesn't matter how wet you are, it's just dry lady parts.