Yes, low thyroid is a possibility, but you mentioned that the chills are especially bad after exercise. Are you drinking enough?? Chills can be the result of dehydration too, especially if you're drinking coffee, tea, colas or other things with caffeine, which is diuretic. You need to drink lots of water while you exercise and right after too. Our fat cells do act like insulation to keep body heat in, but it's WATER that carries the heat and warmth to our cells and tissues in the first place.

Just a thought

Doreen