That's the worst. I had kinda similar issues (12+ day periods, awful cramps, heavy bleeding), after lots of tests, they finally decided I have Adenomyosis. It doesn't sound like that's exactly what you have, but I hope whatever the issues is, it is found quickly! I was diagnosed with that 10 years ago, and even after having a child it's still not better. I only have my period whenever I'm trying to conceive though. I'm on a pill otherwise, but my stupid body only responds to pills for six months or so, then it just rejects it and I have to try a new pill. I've been on every pill out there. As annoying as it is to change the pill that often, it's worth it to never have my period though!
Anyway, ramble done...I'm thinking good thoughts that they'll be able to help you out!