Friend, the yellow color in feces is the presence of bile; this happens when the intestines are over active. The yellow color in the vomit is also bile. When we see vomiting and over active intestines this could be the result of a disorder within the gastrointestinal tract or secondary to a systemic disease. It will be difficult for me to determine the exact underlying cause without a hands on examination and some testing. But, common causes are: Infections, absorption disorders (EPI), liver disease, neoplasia, etc. any of these conditions can also be responsible for the weight loss despite normal food intake.
In this case, unfortunately on history alone it will not be possible to determine the exact underlying cause. She needs to be seen by family veterinarian for a hands on examination, blood work, urinalysis, fecal analysis and +/-xrays as initial screening test. Treatment will be based on exam and test results. In the meantime this is what you can do for the vomiting and over active intestines:
1- Do not give things like Pepto Bismol or imodium. Start her on Pepcid AC (famotidine) 10mg 1/4 tablet every 12 hours for the next 2-3 days. You can buy Pepcid AC over the counter in any pharmacy.
2- No food or water for 8-12 hours. Need to give her gastrointestinal tract time to rest.
3- After 8-12 hours offer a small amount of water. Wait half hour, if no vomiting, offer 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.
4- Follow up with your family veterinarian for a hands on examination as described above. If cost is a concern look into your local ASPCA or Shelter where they often offer veterinary services at a lower cost.
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