Pain in my left side (ribs/breast bone/back a chest x-ray says i've got a collapsed fracture to my d6 vertebrae gp sent me for blood test what's next?

Time should heal: Sounds like you have a compression fracture of d6. Typically it is treated with a brace, pain meds and time. If pain is too high one can always consider doing a kyphoplasty or vertebroplasty procedures.

Pathologic fracture: In a young person, atraumatic fracture is unlikely, especially in a protected area like the dorsal or thoracic spine. Given malabsorption, this is likely a poor bone quality issue--osteomalacia. However, your doc should rule out myeloma, metastatic cancer and infection given your history. Mri and/or ct should also be performed for this purpose. Don't assume all is bad, but don't ignore this.