Frequent urination, especially at night.

When I try to lie down, I have to get up almost immediately and just go a little bit. I went to the drug store and bought one of those AZO test kits, it show up the highest. So, I called the Dr. on call, and she prescribed generica Bactrim (Septra). I hope I did the right thing. It's only for 3 days. I go for my 6 wk. checkup on Thurs. I guess I could have waited, but if this clears it up, then I can get some sleep.