I had cramps like this, and no, it's not normal. I don't have any disorders or diseases, so don't get scared. I just have really heavy, long periods and intensely painful cramps.
I encourage you to go to the doctor!! There are *so many* treatments now for cramps and other menstural cycle problems! Birthcontrol can help cramping, and hormone-regulating pills can help, too. Plus, there are many, many medicines to choose from to help dull the pain of intense cramps. Bextra and Naprocin are just two!
These cramps could also be a symptom of something more serious. That's why you have to see the doctor as soon as possible.
As for your medicine, I'm no pharmacist, but that seems a little excessive. Do any doctors know you're taking that dose each month? Don't get scared about it, just get an appointment. The doctor will understand how much pain you're in when you say how much medicine you're taking. Make sure you tell him/her just how much you take. Then they can evaluate you and get you on the road to less-painful cramps! Who knows, there might even be a more effective medicine that you could try!
In summary, call your doctor! Even your family doctor can help you out with these questions. Good luck!