Help baby B&G losing weight

Hi all new to the forums not sure im in the correct spot but i have a 12 week old B&G macaw and i feel hes losing to much weight. Mostly all of his feathers are in and he is starting to perch and he is mostly out of the cage. He is trying to fly well he is flapping his wings so hard but hasn't got off the ground. He was given to me by someone who couldn't take care of him and hes not weaned. I have other birds but this is the largest one i have. ive been told that when they start to fledge they lose weight and would rather play and fly than eat. He was taking formula real good but now he takes alittle and then turns away.Ive notice his crop doesn't hold as much and ive been told that it shrinks when they start learing how to fly. He uses a water bottle and i always try to keep some type of food in his cage Pellots and millet. I also give him soft foods with a little sprinkle of formula to get him to taste it. He picks at it but not really eating it. I'm starting to feel his breast bone and worried. He doesn't seem to be weak he plays with his toys and climbs up the sofa to be with us and climbs up and down his cage. I dont want to force feed him but i do give him enough formula to see a bump. I'm unable to take him to the vet at this time but looking for some help. He has become part of the family and we love to watch him play and dont want to lose him. Is there anything i can do to put some weight back on him. Thanks and sorry so long

I know you said you cant taking him to the vet... but if you could find any way to arrange that, that would be the first thing. If not at least call an avian vet for advice.

You should be able to feel their breast bone, but it shouldn't stick out.

I am cautious to give advice beyond seeing a vet as there are so many medical issues that could be involved, but there are some foods that can help get his weight up:

Various pelleted "high potency" foods, harrison's makes several.
Boiled eggs.
Peanut Butter.
Mullet and seeds all have high fat, but use in moderation as they don't provide any vitamins or other nutrients.
Chicken, baked or cooked with minimal oil.

Well first of all you need to be weighing him. Get a postal scale at Officemax, a digital one. Weigh him every morning with an empty crop.
Yes they do start to refuse food at this age, their crops will shrink.
Give him a water bowl as well as the bottle. He may drink better from a bowl than a bottle at this stage.
Millet is not enough for him now, its great for a bird on three feedings but he needs more now.
Leave available always: a bowl of pellets, a bowl of large parrot seed and a bowl of fruits and veggies.
I have learned that its advisable to try to get as much as you can in his crop first thing in the morning. It sounds weird but a baby who isnt starving hungry will explore available foods rather than just feeling hungry and begging whenever a human is present.
I know this isnt a problem you are having, its just something to remember.
I think your baby is doing fine. Use your fingers to feel the base of his crop many times a day. If you feel something there, everything is fine, your baby is weaning.
He may well go through a phase where he gets hungry again, feed him whenever he wants it. If it seems that hes given up on eating on his own then take him to a vet.
As long as he is active and bright everything is probably ok.