Amoxicillin and virus

I was prescribed amoxicillin for a sinus infection. (3 x 500mg / day) The good news is that the sinus pain was relieved within two days. On the other hand, I developed several side effects, which seem consistent with other reports I've read on this site. These include the common complaints of diarrhea and upset stomach. In addition, after about two days I started to experienced symptoms of a fever, including general body aches, slight head ache, chills and skin sensitivity, especially on my back. The strange thing is, I don't have a fever (temp. 97.9F). These symptoms seem worse at night. I suppose I could have some type of virus along with the sinus issue, but it seems strange that the onset of symptoms was so coincident with the amoxicillin treatment.