Why am I always cold?

Ever since winter started Ive been freezing every second of my life! even when I'm wearing a long sleeve a sweatshirt over that mittens and slippers in my house and I'm still cold! Everyone else seems to be totally fine but then I'm freezing my butt off and its not fair! I even wear a big sweatshirt and leggings to bed and 3 blankets over me and yet I'm still cold and them temperature in my house is 68 and that temp is pretty warm. It's spring now and its been warm out but I'm still cold! Can anyone tell me why I'm ALWAYS cold!?