Did he vomit again or was that just a once-off? Are you giving him the apple cider vinegar in the drinking water? What are you currently feeding him? Can you check inside his beak again for yellow growths? Also check way back inside his throat.
The yellow urates in the droppings can be a sign of canker. Any other symptoms? Drinking excessive water, difficulty swallowing, losing feathers on the breast, crop slower than usual? So far you've only treated him with amoxycillin for a week (if I remember correctly).
Canker does not always show in the throat, that is just 1 symptom. I would put him on metronidazole 40 mg once a day. So if you can get a 400 mg tablet, crush and divide into 10 heaps. Take small piece of wet bread, cover with powder and feed to him. The lump you are seeing is his trachea, more visible when the head is thrown back as in the photo.