If it is your head, it is in my head too. I have been freezing this winter! I see this complaint a lot of this sub, so I don’t think it is much to worry about, but you may want to talk with your doctor about your thyroid if this persists, as low-thyroid (for me) causes me to be cold, too. I’m just looking forward to summer!
My 2 cents : Could it be a reduction of your metabolism ? It can happen when the body is on glucose metabolism plus “high” insulin level, the body tends to reduce it’s energy consumption. Thus you can feel cold, tired. It means you have not yet entered ketosis.