Are you taking him to an avian vet that specializes in parrots (certified avian)?
Make sure they actually run tests at the vet today and that you get a copy of the results on paper. Try no to let them just look at your bird and start prescribing things based on wild guesses. Possible tests for sick birds: gram stains, fecal cultures/other cultures, swabbing crops, skin swabs, blood work for cbc, blood work for specific diseases which have their own panels and cannot be detected via standard blood tests, x-rays etc....There are others, but during my time with Noodles, we did all of those at one point or another. Your bird may or may not be too young for blood work (don't know how old he is)
Glad you are taking him in, as that is a sign of illness.
Are you using respiratory irritants in your home (Teflon/PTFE/PFOA/PFCs, chemical cleaners, air fresheners, glad plug ins, aerosols, standard household cleaners etc?)
If you are, stop. Teflon/PTFE/PFOA/PFCs can kill a bird even when used on another floor of a home. Bird's respiratory systems are super efficient so things that are safe for mammals are not safe at all for them. If you need alternative cleaners, f10 sc is a good one (it's a concentrate and it makes a ton--I prefer the clear variety b/c it doesn't have soap in it so you don't have to rinse), vinegar is safe as long as it isn't heated up in a coffee pot of something, grapefruit seed extract + water is sometimes also used, as is baking soda. You house should not smell perfumey or fragrant.