Horrible period pain that vanishes in an hour?

I have the weirdest periods and I was wondering if anyone was having anything similar? Every time I start my period (and ONLY on the first day) I have these weird almost episodes. I get the most intense cramps I've ever felt and my muscles are so weak I can't stand and I nearly always collapse completely. I also have hot/cold flashes really badly and intense nausea. The weird thing is though, is that about an hour or two later, it fades away and I'm perfectly fine the rest of my period. It's completely dreadful and I have no idea what to do or how to handle it. My doctor said its just a really sucky period, and booked me an appointment with a gynecologist, but honestly I just want to know what's wrong or at least if anyone else has gone through this. I feel like I'm crazy and none of the doctors even know what I'm talking about.