My son Emmett was put on Omnicef for pneumonia and ear infection. On the second day of being on this drug he had terrible diarrhea, black and watery and he would scream every time he was pooping. He wouldn't sit and would cry if you tried to lay him down to change him-this made me think his stomach hurt pretty bad. Sometimes he would stand there and look at his stomach and just scream. On day 10 of Omnicef he had something on his stomach develop that looked like a heat rash that started off as white bumps then turned red. Two days later (2 days after the drug was all taken) the bumps became bright red and were everywhere. He also had swollen knees that were hot to the touch and wouldn't walk around. We went to the doctor and he said it was a reaction to something he ingested. He said we should give him Benadryl and just watch him. The Benadryl worked for a couple days then stopped working all together. New red spots would come back as soon as the others went away. Three days later we were headed to the ER because of swollen feet, all of his toes connected and his feet were so puffy he wouldn't stand on them, they were also hot to the touch. Luckily we saw a different doctor and he did some blood tests. It turned out he had mycoplasma infection which is also knows as walking pneumonia. He was given Zithromax and was better within 12 hours. The red spots and bumps and swollen extremities were all cleared up. I don't know if he was allergic to Omnicef because he is allergic to Penicillin or if he was just given the wrong drug for the walking pneumonia and it wasn't getting any better. It is definitely worth getting a second opinion in the same day after going through this last week.