Sounds like there's a good chance you have sleep apnea. It CAN be weight-related, but that's unlikely in your case.
Best bet is it talk to your doctor or go to the local clinic... or, just go to a sleep/respiratory clinic (I recommend these guys:
http://irscanada.ca). They should be able to figure out pretty easily if it's sleep apnea or something else, and come up with a treatment for you.