Have Urinary Tract Infection. Difficulty Passing Urine. Pelvic Pain. What Is Wrong?

Hi.....I am a 49 yr old woman who had what seemed to be a urinary tract infection for months. I felt that I had to pee constantly but only a few drops would come out. My doctor took blood and urine samples and said there was no signs of an infection and sent me to a urologist . He did a sonogram of my kidneys thinking i had kidney stones (i had lower back pain and dryheaves a couple times). But he didn t really find anything, Now the urinating problem has disappeared completely but i now have pain in my pelvis , especially on the left side, like a pulling sensation amd also my lower back. I am now scheduled for a CT scan, Any idea what is going on with me? Thanks!