I am sorry for the delay in response. I was offline by the time you came back. In response to your question, when a dog drinks more water than usual it is a sign an underlying medical problem. There are many possible causes. It will be difficult for me to determine the exact underlying cause without a hands on examination and some testing. But, common causes are: An active infection, hormonal disorders (diabetes), kidney or liver disease and even cancer to name a few causes. Any of these diseases can also cause Lexi to loose weight and have loose stool. In other words, her weight loss is directly related to any of these diseases.
As far as the limb being swollen, this could be a completely different problem like arthritis, an injury, etc. Or, it could be the primary cause of all of her symptoms like: Infections, tumors, etc.
In this case unfortunately we are very limited as to what you can do at home. There is really nothing I can recommend for you to try at home that would have a significant therapeutic benefit in this case. Lexi's treatment will be depend on underlying cause. To determine which of the above is the underlying cause your family veterinarian will need to do some blood work (chemistry profile, T4 & CBC), xrays and urinalysis as initial screening test. 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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