UTIs can be triggered by using too much laundry detergent, or by using some types of bubble bath liquid. Another common cause is not emptying your bladder completely when urinating.
If you were prescribed an antibiotic and did not complete the prescribed prescription, the infection may have become immune to them and not completely cleared up.
Talk to your physician about sending a urine sample to test for culture and sensitivity, which will help you find out what type of bacteria is causing the infection