What Kind Of Doctor To Visit For Pain In Hips, Knees And Ankles?

I am a 55 yr old female in good health. I am 5/4 tall and weigh approx. 125 lbs. I am also a Zumba instructor and I teach 2 classes a week. I have been doing aerobic exercise for over 20 years now. I used to teach Jazzercise. My hips and knees and ankles hurt a lot. When I am in the tub I cannot stand up without pushing up with my arms. Its like I am losing strength in my lower body. I can walk up stairs pretty good but walking down stairs is awful. I don t know what kind of a doctor to go to. Any recommendation? Thanks, Karen