Unfortunatley when they start to decline, they go fast. I don’t think it was the medicine. Chams are good at hiding illness. Chances are he was sick for a good while before you even got him. By the time they show signs of illness, they are bad off. They don’t have many defenses in the wild, so pretending they are ok is one way they defend themselves. A sick chameleon makes for an easy target. It is NOT your fault. You have done everything in your power to help him. Take your time to grieve. I know it’s hard even when you don’t have them long. We are here for you.