I want to know the best option for removing a spot of very painful excess breast tissue under my left arm?

Axillary breast tissue can be painful, and is best surgically excised. I most often do this as an office procedure with light oral sedation.

See a board certified plastic surgeon for a proper evaluation. It may require some xray studies but sometimes, these can be removed simply in the office.

Sorry to hear about the pain you’re feeling, Qwisper.
I think that the best thing to do right now is to consult a reputable and board-certified plastic surgeon so that he can personally evaluate you and give you recommendations based on your condition. It’s hard to give advice right now simply based on your description, without any photos to visualize the fibroids under your arms.
Good luck!