Proctalgia Fugax

Every time I'm about to start my period, usually about 2-3 days before I get this incredible painful tightening of my, well, anus. And when I said incredibly painful I mean it stuns my body and I cannot move and have tears flowing. this has been going on since the first time. I never understood it and I thought it was just me until I finally googled the symptoms and talked to my doctor about it and now I'm curious to know if anyone out there in glow/eve land have ever dealt with this?? Or hear of it?