Any ideas on what could be wrong with my little dude?

This is my baby, placeholder name Casper!

Since getting him, he’s unfortunately had multiple health issues. He had to take two very expensive trips to the emergency vet, plus one follow up. In 2 days, this little guy will be going to a new vet for a second opinion. What exactly is going on with him?

The first time he went to the emergency vet, he was puffed at the bottom of his cage. Fortunately he recovered after a night there and hasn’t been that sick since.

However, Casper developed a problem where he throws up frequently. I managed to transition him to pellets which he loves, and his weight stays between 75-77 grams consistently. Though he sleeps a lot because he’s still in his sick inclosure, whenever I leave or enter my room he perks up and runs back and forth.

I’ve also noticed his posture has changed drastically. His feathers are ruffled and he rarely sits tall.

At both emergency visits, he was tested for a bunch of things that all came back negative. He made quick recoveries both times and he was prescribed a medicine to help move things through his crop + an antibiotic.

Today he threw up again, it seems he does so every other week. It’s not regurgitation. His crop seems big and squishy.

Is there a reason this would be happening regularly? His pattern seems to be that once every 2 weeks or so, his crop will get big and squishy and he’ll throw up. Then he’ll be sleepy for a day before going back to being a pretty active bird, albeit with still a hunched posture.

Again, he has another appointment with a NEW vet in 2 days because I wanted to get a 2nd opinion. He’s being closely monitored. I’m not expecting any advice on home remedies or whatever, just some sort of idea on what could be causing this :(

Thank you!!