Clump in breakthrough bleeding

So I am almost 17 and about a month ago I started taking the pill. I am in a sexual relationship and I skipped my period by just not taking the sugar pills and going onto the other row. The past week I have been getting breakthrough bleeding but it was only very light diluted blood, today I had lots of blood and a clump came out. It was about 1.5 inches long and skinny and flesh coloured. I also have bad cramps. Does anyone know what this is??