I've been sick with diarrhea, headache, stomach cramps, and fever for 6 days. Now I have a sharp, constant pain on the lower right side. I took simethicone because I thought it could be gas pains, but it has not subsided. The pain is worsened by moment, laughing, coughing, etc. I have had a fever of 101. Should I be worried that my diarrhea is causing my appendix to become inflamed? Or should I hold out and see if another dose of simethicone works?

It's time to be checked out. IF it is your appendix, do you really want to take the chance that it will rupture?

Diarrhea doesn't cause appendicitis.
Go to a clinic if you can, otherwise an ER.
Stop taking anything at all except clear liquids, and no drugs.