For About A Year Now, I Have Been Having These

For about a year now, i have been having these feelings of cold sensations run through my body. They start out as little cold chills the turn into what can only be described as hot flashes. At the same time they make me feel nauseated. They come at random times and make me feel cold on the inside but hot on the outside. I can't for the life of me figure out what is causing it.