We Have 2 1/2 Yr Old Female With Sudden Onset

We have 2 1/2 yr old female with sudden onset of a botched rash covering her body. She was taken to her pediatrician this morning, who told us that it was just some form allergic reaction. He suggest benedyrl and Zertic. The rash goes away for short of time and then comes back with vengeance. We are noticing also that her joints are swollen. Please help!

Sorry to have bothered you, I wasn't aware of the cost