It sounds very much like you need to get your bird to an avian vet immediately. Any signs of an upper respiratory infection or a sinus infection are serious, and as birds hide symptoms of illness as long as they can, by the time they are actually sneezing, have odd droppings, act tired, etc. they have been sick for quite some time and are very sick at this point. So I wouldn't wait around, I would absolutely get your bird to a vet ASAP.
Unfortunately general vets or even exotic vets that "see birds" do not often know very much about diagnosing and treating birds. It's very important for a general vet to do a fecal smear and a gram stain on the fresh sample you should bring in with you to your appointment, and they really should take a throat/nostril swab and do a culture and sensitivity to diagnose what bacteria is causing the infection and what antibiotic will work. So often general vets do nothing but listen to what you tell them about your bird, they will hear you say that your bird has been sneezing and has been tired, and then they just give you a broad spectrum antibiotic and that's it. They do no tests at all, just give you an antibiotic that they hope will cover the infection your bird has and that's it. And then a week later your bird is much worse, and you have to take your bird back and then they'll give you another antibiotic to try, and so on...That's the difference between a general or exotics vet and an actual avian vet...
I would do your best to find another avian vet that you can get to as soon as possible, but if a general or exotics vet is all you can get your bird to see in the next day then yes, you should go immediately. Make sure you tell the vet everything that has been going on, take a fresh poop sample from the morning of the appointment (clean his cage the night before his appointment and put fresh paper towels down to collect a fresh sample), and please insist on the vet at least doing a fecal smear and a throat/sinus swab to diagnose the bacterium and to prescribe the correct antibiotic that will treat that specific bacterium.
As soon as your avian vet is back then take your bird in to see him immediately, and take all medications, test results (be sure to ask for copies!!!), and paperwork that the general vet gives you to the avian vet. That way the avian vet can make sure your bird was accurately diagnosed and given the proper medication.
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