Is he pooping regular and is his poop normal? Sometimes they can get overfed and get constipated, try treating him with some millet,he could be picky, if he doesnt take the millet then call your local vet and get their opinion over the phone before spending a rediculous price just for a check up. As for the crankyness, it could be his feathers are growing and hes irritated :)

Is he sick? Try feeding him spinach or another kind of lettuce.

Our cockatiel is about eight weeks old and we feed baby bird formula. He was eating regularly last night but this morning he won't eat it. He'll just nibble on it but not fully eat it. He can fly now and we do put bird seed and water in his cage so he can train himself to eat by himself. We occasionally see him eating bird seed and sometimes drink but his tummy never seems full.He can slo fly now. He also gets cranky more often.

Is everything okay with him? Should I worry?