Whats Wrong? i came on but only for a few hours.

I haven't had a proper period since the end of April. I missed my period in the middle of may. I went through on my pill for the next period as i was getting mariied and didnt want to come on during my wedding. The time has now come around now for my period and i came on but only for a few hours. I had real severe back pain all day and could hardly move. I've just done a pregnancy test and it was negative. Really dont know whats wrong