Feeling down in the winter and I don't know what to do about it.

I think I might have S.A.D. but its hard to tell. I have noticed over the past couple of years during the winter months I tend to become more mellow and slightly depressed. For example right now when I wake up and have this general sense of unease. I am becoming anxious over nothing, stressing over the littlest things and becoming jealous at my girlfriend for things that I would never become jealous about a couple of months ago. For example we both have busy scheudles and when she used to tell me she was busy, I'd be totally fine with that. But these past couple of weeks I have found myself getting angry at the fact that shes busy. I don't know why this is happening and I am starting to really resent myself for feeling this way. Does any body know of any way to get out of this funk. I want to stop getting stressed and anxious about nothing and most importantly I want to stop getting jealous at my girlfriend over nothing. Please help.