Switching Birth Control

So I switched birth control back in October and of course it messed up my cycle. But even now, my periods are irregular, I'm spotting throughout the month, and (tmi, sorry) it's always "old" blood. I find I'm always bloated as well. Anybody had this before or know why? It has me worried now. Btw, I switched from one type of pill to another and had about 2 weeks in between switching without birth control