Diffrent kind symptoms and conditions

I have asthma and have been prescribed prednisone several times for it. Every time i take it i break out in an awful acne looking rash all over my arms and my chest and sometimes even my face. it doesn't start until about 3 days after i have started the medicine and it doesn't go away for about 2 weeks and it itches the whole time. I told my doctors that every time they would try to prescribe it and they did not believe me they said no one could be allergic to prednisone but it has happened to me 6 times now and it has never happened before i had prednisone or on many other medicine since then.i finally got them to switch the steroid to a different kind but every kind seems to do it. i had to refuse steroids the last time i was in the hospital for my asthma they just would not accept that i could not take the medicine.