I'm 26 yr old female! Healthy no serious injuries. I have servere pain in my knees and ankles! Worse in the cold or when I walk! What could it be?

A few things. And you should have it checked out. You could have flatfeet which could put stress on ankles and knees, you may have an arthritic condition. It behooves you to get an in person exam. The longer the wait - you could be causing more damage.
Arthritis? This is one of those complaints that is best served by seeing a podiatrist, orthopedic specialist or your pcp. Cold weather can affect joints adversely by creating more stiffness. At 26, this may require a more prospective medical and laboratory examination of bloodwork.