Mineral deficiency. The most important one to take is Iodine. It will warm you up in no time and increase your energy level. Your description of yourself fits me perfectly. I use to be really cold natured. I took a sweater everywhere and slept 10-12 hours per day, plus napped. Now that I'm taking Iodine, I only need 5-6 hours of sleep per day. I wake up energized and looking forward to the day. I used to dread getting out of bed. Take four drops of LugolsIodine in juice twice daily for 2-6 months to correct the mineral imbalace. After that you only need 2-3 drops per week. Go to the Iodine Support Forum hosted by the VWT Team and read the FAQS to learn more about therapeutic supplementation with Iodine.
It is also important to eat some animal fat and cooked vegetables in the winter, especially if you are thin. If you don't like to eat meat, cook your vegetables with butter or ghee. Your body needs the oil right now. You need olive oil and fish oil too.