Most of the body heat that you lose is lost through your head. To keep your extremities such as hands and feet warm, you must keep your head warm and covered. Also, the body protects the core such as the heart before everything else which means that if you keep your core body warm, the excess blood will flow to your extremities to keep them warm. Your body knows that you can live without arms and legs, but cannot live without a functioning heart; therefore, it chooses to keep warm the most important parts of your body--the core. Circulation problems can also be a cause of cold hands and feet; check with your doctor if you think circulation or diabetes could be a cause.
It may be, as #2 points out, just that these are farther from the core of your body. If you are not dressed fro the weather, or you are not consuming enough calories -about 1/3 of all the calories you eat go straight to making body heat- then that could be it. However cold extremities can indicate thyroid problems, or a circulatory problem known as Raynaud's phenomenon. You probably should bring this up the next time you talk to your doctor, just to be on the safe side.
Your hands and feet are the parts of your body that are the furthest from your heart, and your heart is the pump that gets blood to those parts of your body, so there is just further for the blood to go. Everyone's hands and feet get cold more quickly than the parts of the body closer to the heart, which is why people suffer most from frostbite in their fingers and toes. There are various conditions that exacerbate this coldness, for example, circulatory problems, so if you are concerned about this, have a talk with your parents, and see if they think a doctor should examine you.
thank you :)