Erin, when a dog is vomiting their food this can be caused by many different medical conditions. I will not be able to pinpoint the exact underlying cause without a hands-on examination and some testing, I am sorry. But, common causes are disorders of the esophagus (megaesophagus), ingestion of a foreign body, tumors or even part of a systemic disease, etc. to name a few causes. The weight loss is directly related to not absorbing any food or part of an underlying disease. The mucus in the nose could be secondary to the excessive vomiting. Or, she could have a respiratory infection.
In this case, to pinpoint the exact underlying cause your dog will need a hands-on examination by a veterinarian, x-rays. Treatment will be based on exam and test results. In the meantime, this is what you can do:
1- Do not give things like Pepto Bismol or Imodium. Start her on Zantac (ranitidine) 1-2 mg per kilogram body weight every 8-12 hours. You can buy Zantac over the counter in any pharmacy (chemist).
2- No food or water for 3-4 hours. Need to give her gastrointestinal tract time to rest.
3- After 3-4 hours offer a small amount of water. Wait half hour, if no vomiting, offer a small amount of rice (50%) and boiled boneless chicken or ground beef (50%) 4-6 times a day. Keep on this diet for several days then wean into regular diet.
Note: When you feed her raise her food dish on to a small stool to force her to raise her head when eating.
4- Follow up with your family veterinarian for a hands on examination.
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