Just returned from hospital for allergic reaction to bactrim (sulfamethoxazole and trimethoprim) (antibiotic) blood and urine tests fine.i was given multiple antibiotics by iv while there.at the end of my last urination there was blood?

Probably benign: The blood should not be from the antibiotics, but from the urinary infection. Urine and blood tests should be done, including blood clotting studies and a urine culture.

Call your doctor : You should call your doctor and have it checked soon. There are many possibilities of having blood in the urine and it might relate to your recent hospital stay.