Suddenly I have cold feet, why?

Circulation. Usually cold feet is caused by 1) cold weather, 2) poor circulation, 3) neuropathy (which is nerve disease), or disorders that cause the blood vessels to go into spasm like raynauds syndrome. See pcp.
It's winter... Things change in out bodies throughout our life. See a doctor for an exam. It may be a thyroid condition, circulation disorder, or nothing at all.