Omnicef and serious things

Recently, my 12 month old son was prescribed Omnicef for what the Doctor thought was strep throat. Before the medication he had a steady temp of 102 and was very un-energetic. After five does of 1 TSP my son broke out in a horrible rash all over his face, torso/truck, and upper part of his arms and legs. He also got a diaper rash and diarrhea. He also was very bad tempered and moody. This was such a change from his past behavior, even when he was sick. The doctor thinks this is an allergic reaction to the mediation and put him on another antibiotic. I am very concerned about this medication and it's side effects. It seems that eveyone is experiencing some very serious things.