What Causes Diarrhea And Vaginal Bleeding While On Co-amoxiclav?

Hello,
I have been given co-amoxiclav tabletd (1 week's course) for a urinary tract infection (following a 3 day prescription of antibiotics that was unsuccessful and my pain worsened a lot including kidney pain). I am now experiencing diarrhoea as a side effect of these tablets, but I have also noticed some vaginal bleeding (in between periods).
The nature of the infection is undiagnosed as I visited a walk in centre for treatment so they were not able to send off my urine to be tested. And I wondered if it could be a symptom of the infection? I am taking a contraceptive pill and I know the antibiotic can counteract it, so perhaps this is why?
Thanks