UTI symptoms but no infection? HELP?

For the past month I enjoy been have symptoms of a UTI (pressure in the lower belly, frequent urge to urinate)...but no pain...these symptoms started going on for 3 days after a night of rough intercourse. I go to the doctor and they did a urinalysis and urine culture, but no bacteria be found. I then have a pelvic exam, and everything looked fine. I then have abdominal and pelvic ultrasounds, also fine. Yet I still have this constant urge to urinate. Has anyone ever experienced this? Does it stir away on its own? What could be the cause? I suggest you see a urologist. Interstitial Cystitis is a possibility. The just way to diagnose it is through by have cystoscopy.
Drink too much water?