Allergic Reactions to Ethosuximide

My daughter is 8 years old & was diagnosed with Petit Mal Seizures (Absence Seizures) about a month ago. She has had a hard time adjusting to the medication (Ethosuximide). The side effects have been really trying. Now she has developed a rash on her sides and it's starting to spread. She was also recently put on an anti biotic for walking pneumonia. It was something she has never been on before. I took her to the after hours clinic yesterday and the doctor that she saw said that he didn't think that the rash was from the antibiotic because rashes due to an allergic reaction to medication is usually all over the trunk area. He did tell me to stop the antibiotic and treat with benydrl cream. I didn't treat with the cream because honestly it was late and I forgot. Anyway, the rash is worse today and it is starting to spread. I looked up rashes online and it does look like an allergic reaction to a medication. What if it is an allergic reaction to the Ethosuximide and what if they put her on something else and she is allergic to that too? From what I have been told there are only two medications that will treat these type of seizures. Anyone else had any issues like this and if so how did it turn out for you?

Concerned Mom