Recently, my feet and hands have been really cold. could it be my metabolism is slowing down?

Could be: Cold hands and feet can have many causes, most of which are not serious, but they can be annoying. Low thyroid can cause this and should be checked out. Low blood count, vasospasm of arteries, raynauds phenomenon are all potential causes. Only your doctor can really help you sort this out. An exam and a few blood test will go a long way in helping to determine what is going on.