Urinary Tract Infection - I was diagnosed with a UTI on Tuesday, and shortly after began having back

Hi, brchra!
I agree with Missy. If a Culture and Sensitivity test wasn't run you may be on an antibiotic that's not effective against the bacteria causing your UTI. The pain in your back could be an indication of kidney involvement so you should get a professional medical opinion ASAP.
Best regards and I hope you're feeling better quickly.
Wildcat

You need to go back to the Dr or to Urgent Care. It’s possible that the antibiotic they gave you doesn’t target the right kind of bacteria that’s infecting your bladder. Usually most people see a big improvement in symptoms within 3 days of starting an antibiotic. Make sure you’re drinking lots of water, to flush out the bacteria.

Don’t let it drag on though. Years ago I waited too long to get medical attention for a UTI; I ended up with a kidney infection and spent a week in the hospital on IV antibiotics. It was extremely painful. You don’t want that to happen.