What Causes Left Abdominal Pain, Increased Appetite And Sickness?

My son has been complaining for over a week with abdominal left sided pain went to GP a week ago prescribed co amoxiclav 1x 3 daily plus naproxen 2xdaily. He still got pain not all the time but on and off,he said he feels slightly sick but got the feeling he s hungry,he had his tea and drinking plenty fluids.He is 28yrs old.