What Causes Fever , Diarrhea , Loss Of Appetite And Sinus Infection?

I have had the following symptoms for three days now. 1) fever ranging from 99.6 to 100.8; 2) extremely watery diarrhea; 3) no appetite; 4) sinus infection with green mucus and chronic cough. My big concern right now is the watery diarrhea and the potential for dehydration. Is there anything over the counter that I can take? Thank you.