It is very difficult to change doctors sometimes. Another thing you could do before "giving up" on your existing doctor is writing them a brief (1 page) letter. Make sure the letter is not accusatory in tone, but be specific as to what you want and need from your current/old doctor.
1. You have enjoyed being their patient for X years.
2. You have told him/her of your new symptom on the past X visits.
3. He has not done anything about it.
4. You really need him/her to address this new problem or you will have to seek new treatment with a different doctor, this is very serious to you.
5. You would like a Referral, or test, or X treatment.
6. It is very frustrating and sad to think about leaving their practice.
Above all, be Polite, thankful and gracious! You don't want your old doctor to "bad-mouth" you to a new doctor because your new doctor will get your old doctor's medical records and read them or talk to the old doctor. Depending on the size of your community, the new doctor may know the old doctor personally too.
TOS and Pain Management is not a big field so its likely that they know each other and they could and will talk to each other.
Word from the "been there-done that" club.