I would go ahead and tell your mom as UTI's are caused by many different reasons, sex is just one of them... and that is why young boys and two years old girls get UTI's as well... and they are not having sex.

A simply practice may help lesson your risk at getting another UTI (after your present UTI is properly dealt with) and it is easy - just make sure you go potty before and after sex, by releasing your urine you are flushing away foreign matter, some that comes from having sex... and remember what is safe to be in his body may cause physical issues in your body, a good argument for always using a condom during sex.

Drinking Cranapple or Crangrape juice helps to deplete the body of the bacteria that causes UTI's... the over growth of bacteria attaches to the cranberry thus allowing the body to expel it during urination - this is an old Native Indian cure for female issues.