Just the act of having sex during a girl's period doesn't cause a urinary tract infection. UTIs are caused by any of a number of bacteria that can get into the urethra, both bacteria that usually reside in the male or female genital areas and sexually transmitted diseases. Your doctor will have to give you a prescription for antibiotics that will cure the particular type of infection you have. If it is found to be an STD you will both need to be treated at the same time so you don't wind up passing it back and forth.Meanwhile, try to drink lots of water and 100% cranberry juice to keep the urine as dilute as possible so that it doesn't burn so badly. I hope tis helps.