Can multilevel, severe thoracic disc desiccation result in upper left back pain after eating? Thanks.

Look at GI tract. If this connection between eating and pain continues to hold true, look for a source within the gastrointestinal tract. Esophagitis and gallbladder disease are two possibilities.
Thoracic back pain. Thoracic back pain can occur from disc herniation, degeneration of the discs and inflammation where the rib heads insert on the spine. It is an unusual symptom for degenerative thoracic discs to become painful after eating. See a spine specialist or neurosurgeon to help find the source of pain and treat it.
Probably not. Thoracic degenerative disc disease may result in some back pain but it wouldn't be related to eating. This could be due to something wrong with your gastrointestinal system and you should see your doctor.