I just keep bleeding.

My gynocologist recently switched me from Yasmin to Yaz. Probably about 3 months ago. I wasn't having any problems until this month. Well, you know the week when you only take 3 active pills and then 4 inactive. Well, of course, that was the week I was supposed to get my period. And I didn't. So that Sunday that I was supposed to start up on my birth control again, before I took my birth control, I took a pregnancy test and it came up negative. So I was like okay, no problem. I took my birth control and then the next day, I started my period. It was weird, but I was just happy I got it. So I had it normally for about 4 days. Monday to Friday. Then I didn't have it Saturday or Sunday, so I thought I was done. Then Monday comes up, and I start having a brown discharge. I thought that was pretty normal too, because it was just dry blood or something, right? So I have it all of Monday. Then all the sudden, I wake up Tuesday morning and there is blood everywhere. It's been about a week now and I have been bleeding everyday VERY heavy with very painful cramps, which is weird, because I never bleed heavy and I never ever have cramps. Some people are telling me it's a miscarriage. Which I highly doubt because my boyfriend and I very rarely have sex without a condom along with the birth control. I mean, we've had sex without a condom, but have never gone the whole way. Not to mention again, I take my birth control everyday the same time of the day.

Does anyone have ANY clue? I mean, I know I have a gyno appointment Thursday, but I'm so worried it could be something serious.