I would definitely take him to the vet tomorrow, and tell him all that you have told us. He may have an infection from the formula being too cool. For a macaw I have the temp. 106-108 and stir it to be sure there are no hot spots in it. At his age I would have him on 4 feedings a day. I would rather him have 4 feedings and eat a little less that 3 and stuffing him. He should be getting approx. 10% of his body weight, like Carole said. I would just have 1 person handfeeding him, 2 if you have to have someone else, and I would have him in a quiet area with no one else around when you are feeding. You need to have your full attention on him, and he needs his attention on eating instead of watching what is going on elsewhere.
My thoughts is that he is not eating because it's too cool. Some birds, usually the larger ones will refuse to eat cool formula. Also, like Carole said I would feed the Zupreem Embrace formula. It's probably one of the best formulas out there. If there is any way you can keep him warmer it would help also. He should have been kept in a brooder and if you don't have one, try to keep his temp. around 85. If he acts like he gets too warm you can lower it a bit.
Definitely keep that vet appointment. Hope he gets on the right track and grows up to be a wonderful bird for you!!