Is Spotting Of Blood With Vaginal Discharge Sign Of UTI?

Hi iv had lower back and stomach dull aches today mainly in my lower back and yesterday after i went to the gym i noticed a spot of bright red blood mixed with my vaginal discharge (discharge is white and drys on my underwear to a creamy colour) I was diagnosed with PCOS last year and my last period was about 6 weeks ago my periods are very irregular and i also have prolonged periods that can last a month or so at a time. Anyway what im trying to get at is can a urinary tract infection cause the spot bleeding i had yesterday i have never experience that type of bleeding before .....additional infomation im in a faithful relationship and had a std test about 5 or 6 months agos which was all clear