I still wonder if he needs that ivermectin? It's about the only thing he didn't get.
I think he should drink more water, but wonder if the Amoxicillin in the water discourages him from that? Perhaps there's a bad taste? You know, you just guess.. does he even need an antibiotic? 4 days current Amoxicillin.
What would you be treating with the Ivermectin?And, I'm not sure if the 'crop is emptying', or exactly how you check for that? I mean, his digestive system seems to work fine and he will eat plenty, may even be regaining weight.
What Amoxicillin do you have? Is it tablets, capsules, powdered mix? Generally Amoxicillin comes in tablets or capsules and given orally and dosed by weight. Amoxicillin dose is 57mg per pound of weight given orally twice a day. I have never been able to get Amoxicillin tablet or powder from a capsule to dissolve/mix well in water. It may be bitter too, if he's not drinking the medicated water, then there's no benefit.
His crop is located on the right side of his breast, you should be able to feel that when he's been eating. Check it tonight when he goes to roost, then feel of it again first thing in the morning before he's had anything to eat/drink, the crop should feel flat. What we're looking for is that his digestive system is functioning fairly well. A crop (the pouch that hold food) can become boggy or sour. Sometimes the gizzard can be impacted as well. A crop issue can cause a lot of problems, but is usually a symptom of something else going on.
The closing of the eye(s), the lethargy and missing the bowl sounds neurological. Have you noticed if his eyes are misshaped or turning grey? Has he been in a fight or suffered head trauma. Have you added new birds within the last 30 days.
Marek's disease always comes to mind when a bird is having issues with seeing/missing the intended target. He's 3 yrs, so a bit older than you would normally see an outbreak, BUT it's still a possibility.
The Poultry Cell has vitamin E and B1 which can help support neurological symptoms, but they are not a fix all. If you can't find that, then you can use human vitamins, just look at WalMart, CVS, etc. Get 400IU Vitamin E and B-Complex. Give him 1 Vit E gel capsule a day and 1/4 tablet B-Complex.