oh my freaking god

I'm grinding the shit out of my teeth in my sleep and they hurt SO bad. I have a permanent retainer in my mouth and it's like I tried to rip it off. 
Is there some kind of mouth guard I can buy? Where? Do they come in smaller sizes? Can I wear one with a retainer? My retainer is glued to the back of my teeth and pretty much never to be taken off. This is really awful pain. And it's loud and my SO is telling me about it and he'll wake me up because it sounds like I'm chewing on rocks.