What Causes Continuous Bleeding After Taking Morning I-pill?

I had unprotected sex two weeks ago on monday and took the morning after pill the day after. I am on the pill but i hadnt been taking it regularly as i missed a few days by mistake which is why i took the morning after pill. Ive been on my period ever since which will be three weeks on monday and im not getting any lighter on it. Why is this im worried? Please help