Greetings, I am Dr. Pat. I have worked with birds exclusively for many years.
I am sorry no other expert has taken your question. We all come online at different times, I have just logged in and saw that you have not been answered. I hope I can still be of assistance.
Vomiting can be from GI obstruction (common in birds that have access to grit), toxins, viral/bacterial/fungal/parasitic infections, nutritional deficits, and so on. It can be very difficult to sort it out. He should certainly have a sample taken from the crop (very easy if the vet knows what they are doing) to check for common problems such as soiral bacteria. Macrorhabdus, yeast, bacteria, protozoans. This is quick and easy to do at the vet's office and should not be expensive.
There should be no reason that he is hurt or depressed after the vet visit. Again, you might call around and see if there is a more experienced vet.
Was the bird tested for Psittacine Feather and Beak disease?
Was she tested for Borna Virus? This is fairly common in lovebirds and can be associated with vomiting AND feather issues.
What was the medication?
In vomiting birds, they must be on injections, for obvious reasons; and they need to have fluids/electrolytes also as injection SC.
The feather loss could be from severe respiratory infection. It could also be systemic.
Can you tell me more about the bird?
How long has this been going on?
How long have you had him?
Where is he from?
Any accidents or trauma?
Interactions with other birds/pets/children/guests?
What is the usual diet? has it changed recently? Any people food or treats?
Has the bird gotten into anything?
If you feel comfortable with it, examine the bird thoroughly, using gentle restraint via washcloth or hand towel: do not restrict the chest or hold around the body. Check the eyes, nostrils, mouth and beak if possible, having a good look in there for mucus, redness, masses or anything else unusual. Palpate the tummy for pain, fluid, lumps or anything else (eggs, if female or unknown). Check all the joints for swelling, pain, and mobility. The feathers should be parted to view the skin, muscles and skeleton below; this can be done using a q-tip with isopropyl alcohol or KY gel. Look for bruising, lacerations, injured feathers.
Your job is to keep the bird warm, safe, quiet, and confined; and to provide adequate hydration and calories.
Move the bird to a box or carrier with soft towels in the bottom, no perch, and food and water in low bowls that can be reached easily. Put the whole thing on a heating pad on low or medium. Check it frequently, no overheating allowed! Keep the unit partially covered, warm and quiet. White paper towels or white cloth towels will show the true color of the droppings. Small animal/reptile boxes are great for this purpose.
The bird, bowls and unit must be kept very clean.
Here are some helpful links:
IF HE IS ABLE TO KEEP LIQUIDS OR FOOD DOWN:
Do not try to force food or water. Pedialyte or electrolyte replacer can help but many birds do not like them; when in doubt, plain warm water is best. They can hydrate from oral fluids almost as quickly as IV if the GI is functioning properly. You can offer warm cooked rice, pancakes, cornbread, grapes, melon, greens in addition to normal food.
If your vet does not work with very many birds, you should have a second opinion by a more experienced vet. I really must stress that you need a bird-experienced person, and not just a vet who advertises that they care for birds.
You need to take your bird to see an avian-experienced veterinarian ASAP for complete examination, diagnosis and appropriate treatment. Check
https://aav.site-ym.com/?page=basiccare click on "find a vet"
Feather issues can be caused by a multitude of things, including bacterial skin infection, viruses, fungal infections, allergies, metal poisoning, hormonal flux, psychological or combination of these factors. The difficulty is diagnosing the problems and assigning an intelligent treatment plan. Your vet will want to run a number of tests so that appropriate medications can be prescribed.
Inflammatory skin/follicle disease is common. The causes can include local infection, metabolic problems, or even intestinal parasites. It can also be a prime area for even more serious problems like skin cancer. An avian-experienced vet should take a look at the poor bird, and run some tests.
If this were my patient, and money no object, I would start with complete fecal analysis and direct smear, stained with Sedi-stain and unstained for multiple parasites, fungi, spirals; direct smear stained with Sedi-stain and unstained of the crop and feather pulp; bacterial culture and sensitivity of the feather pulp, feces and crop. Depending on the case I might do a fungal culture. Routine blood work is necessary to rule out other issues. There are MANY DNA/RNA tests for bird diseases--and testing for Borna Virus would be a good idea. Ultrasound is often more informative than radiographs and does not require anesthesia (ask your vet about this option). Generally I start them out on medications as indicated by the tests.Generally I start them out on injectable antibiotics and an anti-inflammatory such as ibuprofen.
IMPORTANT Check the website for the feed you give, there have been many recalls; or check this link: