What Causes A Vaginal Discharge After Intercourse?

I have been taking Cerazette for four weeks now, I was a bit silly and as it had been a while since stopping on Dianette i was anxious to start taking the pill again so didn't wait for the first day of my period to do it, I am on my fourth week, and since yesterday have been having a strange pink coloured discharge, it started after some vigorous sex, I havent had a period since roughly 2 weeks (maybe less) before starting this pill. Anyway today I had a small gush of a pink watery substance. I am wondering if this is down to the new pill i am on and I should wait another day before i get worried for it to sort itself out, or is there something wrong?