Omnicef and sunburn

My 9 month little girl took omnicef and developed a rash after her second dose. I took her to the doctor - they thought she had either roseola or hand foot and mouth.....By the time I got her home that afternoon and some time had passed - it developed more and looked awful. I called the doctor back and she informed me that with roseola or hand, foot and mouth it would get worse before it got better. That night my baby was very uncomfortable, could not sleep and kept trying to scratch the rash through . The next morning, I called the doctor back because by this time she looked like she had a horrible sunburn and it continued to worsen. The pediatrician then thought she was having a reaction, suggested benadryl for two days and then switched her to augmentin. We will begin taking that tomorrow morning - I am a little nervous because I hope not only that it will work but that she will not have any side effects like she had with ominicef. As far as taking omnicef, my other children have taken it and they were fine -but as for my baby I had it documented on her chart at the doctors office and at the pharmacist so that they will stay away from all medicines that are in the omnicef family. I hope that I will never have to see this again nor deal with it. Jenifer