Hi there. My girlfriend and I have an active sex life. She is also on the pill. Her last period came exactly on the day it was supposed to, but oddly enough it only lasted one day.

What exactly could cause this? I will say she had a medical procedure (lancing of the lubricating gland inside her vaginal wall) done about a week before hand. I imagine stress in general, let alone vaginal stress can cause an abnormal cycle?

Any thoughts? Thanks!