Question about period after baby?

So my son is 9 months old, I recently got back on birth control about a month and a half a go. My period comes when it's on the sugar pill part of the pill pack, but just now I'm in the middle of the pill pack and I'm having the heaviest period I've ever had... when I just had a period two weeks ago. Like clots and everything is coming out of me so much is this normal? I do have sex regularly and my husband generally doesn't pull out I'm not sure if that has anything to do with it but this has never happened to me before. Could it be breakthrough bleeding?