long period starting on the pill?

i started the pill almost 13 days ago, on the first day of my period just like I was supposed to. But I’m STILL ON MY PERIOD almost 2 weeks later, and still having the occasional cramping blood clot too. This happened when I took Plan B one time, is this how my body is going to respond to estrogen/progesterone forever or is this just a first time thing? I got on birth control because of my insanely heavy and painful periods, so I really can’t handle that makes it anything worse.