Is this a uti or something more serious?

i am at 19 year old girl who has been tested for stds (very recently) and doesnt have any. i went to the doctor last weekend because i felt like i needed to pee alot and not much was coming out. i didnt have any pain or anything but the doctor said i had a high white blood cell count and there was a little blood in my urine so he was comfortable putting me on antibiotics. he told me to call back on wednesday to get the results of the urine test but they never called me back. its day 6 of the antibiotics and i still feel like i have an urge to pee more frequently then normal. i still have tonight and 4 more days of antibiotics. should i be concerned? is there something else this could be?