I also have a minor but soemtime itchy rash, just on my forehead.
Eosinophils are white blood cells used for specific purposes.
If you have developed a rash at the same time, it seems likely that the rash and the eosinophils are related. You need a careful history and physical. I'd want to take a look at your rash, and it might help to take a biopsy of it. Depending on your travel history, it might be worth doing a stool specimen and a blood test for parasites. Sustiva seems like a possible cause, but less likely if you had a high count before starting.