bactrim may not work after the first pill. your doctor could have given you some pyridium to help the urinary pain but since he/she did not keep drinking tons of water and take that bactrim as prescribed. unless you had a urine culture there is really no way to know if bactrim was the appropriate antibiotic for this particular uti but if you do not improve or getting worse there is a very good chance that the antibiotic may need to be changed or other causes investigated that can cause uti-like symptoms.
i started my first bactrim pill today and now it hurts worse then before when i pee is that normal