What could case pain in spine under bra? It's different pain than the bulging disks I have and much more severe, not muscular at all. I'm miserable

Varies. There are a number of potential causes including superficial things like local irritation of the muscles in the back, or deeper things like facet arthropathy, or a pinched nerve. I would not hesitate to be seen and thoroughly evaluated.
Thoracic disc. Thoracic disc herniations are not as common as low back or cervical disc herniations, but when they occur they will produce pain radiating from the spine along the course of the ribs on one or both sides.