What are some causes of back pain? (plz read)?

since monday i have been on antibiotics for a UTI. my results came back negative but i am still taking the antibiotics, and all my symptoms went away but today i started getting back pain. its on my side on the left and it hurt more when i move or turn the wrong way. i jogged on treadmill today and i felt fine it actually went away and then came back. i have a doc appointment with a urologist on june 27 but does this sound serious?