There are many causes of high red blood cell count:
According to the article, dehydration can result in increased red blood cell concentration.
It depends, but the fluctuations in your labs suggest that it is more spurious than real. You can discuss with your doctor if you should retest or leave it alone. However, do not get distracted too much by this single lab test. It is important that you and your doctor refocus to try to solve the problem of why you are having leg pain and tenderness.