What Causes No Period During Yeast Infection?

well this all started 3 weeks ago and they thought i had a bladder infection so they gave me medicine and that didn't work so finally i got tested and it was normal and than i missed my period and so finally they did a pelvic exam and i have a bad yeast infection and an abnormal pelvic exam and it was level c and they said i wasnt pregnant and have pissed my period by almost month now and when i had sex we used pertection but i want to know why everything is coming out like this?