Does Sinus Medication Cause Neck Pain And Soreness In The Soles?

My nine year old son has pain in his neck, the bottom of his feet are sore and says he feels like his skin is on fire even though he is cool to the touch. He is currently taking Amox-Clav Es twice a day (600mg) for a sinus infection. Do you think this is a side effect from the medication or is it possible something else is going on? He has not had any bloodwork done.