I'm sorry your macaw is sick.
You mentioned the cold snap, was he kept outside?
I agree with you and the other members , this is cause for concern. And an avian vet is needed, with blood work abd gram stain minimum.
As stated above, get a digital kitchen scale, and track weight daily till resolved to see how ( hopefully treatment by new vet ) is going, and that the bird is not loosing weight.
Sick burds need extra warmth, it very helpful with healing, and to save them calories. Sweeter heater as found on Amazon is whst I use, tge smallest one and set back from cage. Its radiant heat and that's the best kind. By support warmth i mean 85f , so a supplement heat source is needed. I also turn my home heat up to 78.
Sick burds also burn 3 times their normal calories. So it is helpful to supplement with baby burd formula made thick like yogurt and served warm, never force. Many burds will take from syringe abd like. About 20ml at a time should be good for your size bird. If still eating on own then once or twice a day or support. An hour before bedtime helps them overnight.
Sometimes chronic zinc toxicity or heavy metal poison can present like this. Vet would have to do a blood test an x ray looking for metal in digestive system. And so many infections can all have the same symptoms. So only a veterinarian could help identify.
I've had seriously ill parrots, and quick veterinarian care, supporting warmth:, supplement feeding has saved them.
These are definitely serious act now symptoms.
