I'm on a pill which I take for 28 days then have a 7 day break where I have a period. I'm not due for about 10 days but last night I got really bad cramps and a bad back, exactly the same feeling as the first day of my period. I had a bit of spotting but it was brown blood so not fresh (sorry if TMI!) and that's it. Feel normal today, period hasn't started. This has never happened before 
. Does anyone have any suggestions of what it could be?