Lisa,
I am exactly in the same boat as you, and I am on the last day of Trimethoprim 200mg today, after trying lots of others.
I have had a scan, and it showed my bladder was not emptying all the urine, which caused it to stagnate.
This caused peeing frequently, and pain when passing.
They also found that my prostrate was enlarged, which could also be a factor, and have been given Flomaxtra XL 400mg, prolonged releasing tablets.
I have to got for another test next Thursday, to test the speed of flow of urine, or something like that.
Let us know what the doc says, and calm down, and dont worry to much.