Okay this is horrible...first of all, you shouldn't EVER spray Chlorhexidine all over your bird's body or any other living creature's body, as it is well-known to cause blindness if it gets in the eyes, deafness if it gets in the ears, and severe damage to any mucous-membranes it comes in contact with!!! It's Hibiclens, if you're familiar. It's used as a great wound disinfectant and protective barrier from microbes during surgery (like Betadine used to be), but it's extremely dangerous when it comes in-contact with any mucous membranes, the eyes, or the ears...So there's no way you should be "spraying" it all over your bird's body...You can Google this yourself to see what I'm talking about...
Secondly...Why did this vet prescribe the Doxy? Did he get a positive gram-stain/culture for a bacterial infection? If not, why did he prescribe an Antibiotic at all? If it's "just in case" or whatever, then I'd stop, as again, if your bird smells yeasty, he most likely has a yeast infection and antibiotics can make it much worse. You need to find another CAV and get the test results/records sent to them, and go from there. By the way, a yeast/fungal infection will show-up on a gram-stain under a microscope, but only if the culture/swab was taken from the source of the infection. So if your Vet did the gram-stain from a fecal sample, throat sample, etc., but the yeast infection is in his crop, then he wouldn't have seen it...Also, sometimes if the yeast/fungi is in the early stages, it has to be allowed to grow, so it wouldn't show-up on a gram stain, you have to plate it and grow it...However, if your bird already smells like yeast (sour smell, can't mistake it), then it's not in the early stages...
In the meantime, please get some Benebac or Avian Probiotics and start giving them to your bird daily, as they will help to treat a yeast/fungal infection, as well as to protect him from the antibiotics making a fungal infection worse...