What Causes Heavy Bleeding & Headaches During Menstruation?

Hi i'm am 18yr old female, I had sex with my partner about a week before my period was due, after that i ended up missing my period for a month straight, on the 5th of Feb. it started and Ive been having heavy bleeding ever since its been exactly 2 weeks now. I've had no cramping at all and as of recently i think about 2 days now, I've been having headaches off and on now. I'm quite worried and i would like to know if i can get some insight on what may be happening to me.