I'm very far from an expert on singing, but I can attest to the value of having an expert singing teacher. You sound like an experienced singer, but it's possible that you have picked up some singing habits that haven't helped your voice. A good singing teacher could help you with that. I would recommend someone with a serious classical background, even if that isn't the kind of music you want to sing. You need someone who has really mastered the technical aspects of voice production.

It would probably be a good idea to see your doctor as well to see if there is anything organic that is affecting your voice. He or she may be able to refer you to a vocal therapist.

You might also want to consider Alexander technique classes. A lot of musicians swear by them. I have done a bit of reading on the subject, but haven't had the time to start yet. I intend to start in the new Year, however.

Good luck.

Edmund