My question is, why my hands and feet are always cold specially when is winter time?

Probably, you have - Raynaud's disease or raynaud's phenomenon. Some people, otherwise normal, can also have it. Some smokers have such a problem. A rheumatologist will be one to DX the raynaud's disease, and treat it. Do your finger tips turn blue as well? In most cases, its just simply due to the cold when blood vessels in the skin constrict to keep the body's temperature stable.