I have pain in my back on the left side after having an uti for 2 weeks?

See your doctor: You should not have had a UTI for 2 weeks if you were being treated correctly. Although without other symptoms it is less likely that the infection has reached your kidneys, but this can be kidney stones, ureteritis or something completely outside the urinary tract, like an ovarian cyst, etc. Go and get diagnosed. Best wishes.