I started walking daily and now my knees hurt very badly, haven't walked in 4 days to relieve knee pain and they hurt just as bad or worse. why would my knees be hurting like this just from starting a daily walk?

Varies: There are a variety of reasons for a person to have knee pain with walking and an exam and appropriate studies can usually determine the cause, so I would not hesitate to be seen. Arthritis and internal derangement of the knee would be uncommon in a 37 year old without injury. TFL syndrome is most common cause, which is a tendonitis of a tendon on outside of thigh that inserts on outside of knee