Omnicef and eye infection

My son was recently diagnosed with a sinus and eye infection. The doctor prescribed omnicef and since his initial dose he has had diarreah along with a horrible diaper rash. In addition to that he has been vomiting within 1-2 hours after taking the medication. I called the doctor to switch meds and I am horrified to report that they told me to continue to give him the medication that these were normal side effects. I don't need a PhD to know that my son is not ok after taking this medication. Unfortunately, our regular pediatrician is out of the office for two more days. I cannot believe that these doctors whom we pay could make our children worse. DO NOT GIVE YOUR THIS MEDICATION!!!