What Causes Heavy Bleeding, Cramps And Headache?

im 18 years old and I have been off my period since the 25th of Dec. On the 29th I woke up and blood was every where and nothing else happened. The day after that I didnt have anymore bleeding but it was a dark liquid. Yesterday I woke up with a little bleeding but then later that day I began to cramp. I then went to the bathroom and I was bleeding heavily. And Today I am experiencing the same thing but I have a headache...