Switched pill brands!!

So I had been taking birth control for 6 months and have been taking the active pills only- never once getting my period because of that. But I recently switched brands a month ago and continued only taking the active pills but two days ago I got terrible cramps that felt like period but no blood. Then yesterday I had sex without a condom (but was still on birth control so leave me alone I know the risk and it's my life) and I ended up bleeding and little clumps came out like I started my period, and today I am bleeding but not heavily or as I usually have while on my period- and have terrible cramps. But what I don't get is the fact that I have never stopped taking active pills yet I got my period.... HELP.