Suggest Specialist To Be Consulted For Pain In Knee And Back

Hello..i have been going to PT for about 4months for venous knee, back issues... My PT has found that my tailbone is hooked as well it is mobile.. she has been trying to get it straight. Some days it is on the left a 1/2 a inch and other on the right. I have neurological pain down the right leg. I used to have it on both. Is this possible that it is loose? and what kind of doctor should I see?