Dental clinic symptoms and conditions

My child was prescribed Omnicef for an ear infection on Tuesday and we ended up taking him off on Friday night. He is normally a happy, hyper, normal 3 yr old but he became very mean!! We didn't know what was going on with him. We just thought that maybe he was acting out, until we talked to some one who knows about food allergies who asked if anything was different in his diet. The only thing that was different was he started this new anti-biotic. He had an allergic reaction to Amoxicillin and we told the doctor. but he still put him on this medication anyway. Our son changed so much in this last week it is just unbelievable. On the second day of this medication he actually tried to bite some older gentleman at a dental clinic. Just not his normal behavior. He didn't sleep well, would literally kick, hit, punch, pinch and bite us and his siblings. Since we took him off this medicine he is finally acting like his normal only self. We had not realized until he started to giggle about something that he had not laughed since he started his medicine. There is no way that he will ever take this medicine again and after reading all the information on OMNICEF I do not understand why they keep pushing this drug since there are so many harmful side effects (half of which they do not list)!! I just hope that this has not done any other damage to my son internally as well...