What Causes Stomach And Leg Pain In A Child?

My 8 year old son was prescribed 2 rounds of Amoxacillan for strep throat, as after having taken 6 days worth he became ill with all the same strep throat symptoms again - fever, throat pain... He was prescribed a stonger dose of amoxacillan again for 6 days. Since finishing this second round and even several days before he began to complain of severe stomach and leg pains. We even went so far as to have an ultrasound done on his abdomin. The radiologist said that his appendix was swollen and perhaps this was the cause - my son was admitted to hospital. The surgeon asked us to wait 48 hours to see if the pain subsided, it has not. 1)We are having him tested for the chance of ruematic fever tomorrow morning - to rule that out. 2)I suppose we need to wait and see if this really is going to become an appendicitis, based on if his stomach pains worsen. 3)At the end of the day, I suspect that the stomach and leg pain he is suffering has been caused by the antibiotics. Any ideas?