Does Medication For UTI Cause Itchy Red Rashes On Legs And Abdomen?

Had symptoms Of a UTI and went to an urgent care clinic on weekend for help. Was given a urine test and they said no nitrates but lue showed positive. Was given Bactrim for the uti for 10 days. Took all of it and on the 10th day broke out on my legs with an itchy red rash. Looks like pin head type dots all over my legs and abdomen. Not raised at all. No fever or any other symptoms. Never took this drug before. Is this just a side effect or should I be concerned and go to my doctor?