Sorry I didn't get the PM till now. Doesn't sound like you're having fun.
It sure does sound like the tooth is reinfected. Upper molars do have an extra canal that needs to be cleaned and filled. It's not always easy to find and that's why root canal specialists (endodontists) typically have a big microscope handy.
Did your guy do anything wrong? I have no idea. Would I, at this point, ask to see an endodontist? Yes.
Folks, I'm very comfortable with GP's doing the vast majority of procedures but if you EVER have doubt whether you'd be better off in a specialist's chair, ask. If not satisfied, ask again.
For reference, the specialties are:
Pedodontics: kids
Orthodontics: correcting tooth positions/facial deformities
Periodontics: periodontal disease, gum/bone grafting, implants
Oral & maxillofacial surgery: jaw fractures/trauma, wisdom teeth, bone grafting, implants
Endodontics: root canals
Prosthodontics: complex dentistry, full mouth rehabs
Oral & Maxillofacial Radiology
Oral & Maxillofacial Pathology
Public Health
There is no such thing as a "Cosmetic Specialist" or "Implant Specialist".
/rant
I hope you feel better soon.