Am wondering about UTI causes.

How is it that unexpelled urine can cause a bladder infection? I mean, urine is sterile, so how does that happen?

Also, my UTI sx are so subtle that I put off going to the Dr. cause I'm just not sure. Have taken 3 antibx in the past 5 weeks.

I don't have pain when I urinate, but I do tend to go more often and there is a little urgency involved. I guess I'm just avoiding the doc cause he may send me in for some kind of surgery to help the bladder empty completely.

What to do What to do?