Sore tongue, almost like it's too big for my mouth?

I wake up every morning (for about the last month) and the sides of my tongue is so sore - when I look at it in the mirror it has the imprint of my teeth on both sides, almost like my tongue is too big for my mouth and sits against my teeth all night! It hurts so much that the following night I have to try and keep on my one side so my tongue falls naturally the one side it is least sore on. I'm getting a bit worried as it has been going on for a few weeks any idea what it might be?!