I walked with my foot inverted to "fix" my flat feet. i think this caused my hip/back pain for the last 8 years. which doctor should i see for this?

Osteopath : I would recommend a good osteopath (do) that practices osteopathy. If you can't find one, a chiropractor is a good alternative.

The body is a unit: A doctor who well versed in biomechanics, usually an osteopathic physician, physical medicine & rehabilitation specialist (physiatrist), chiropractor, or orthopedic surgeon. A team approach integrating the expertise of a podiatrist may be the best approach. The body is a unit; structure and function are reciprocally interrelated and a doctor who understands this is more likely able to help.

Physiatrist or Pain: A musculoskeletal physician (physiatrist, pain management, sports docs) are best to address injuries and pain associated with biokinetic deficiets leading to pain in multiple body regions.