Is it safe to mix prednisone with zyrtec and benadryl?

I've had a really horrible allergy cough lately wich sux cause I have asthma and i went to the doctor she said not to worry told me to take benadryl, but then it got worse, so i went back litterally a week later, a diffrent doctor listened in on my chest and back and said I was really breahing bad and my vital signs showed my oxygyn was kinda low (Like 92), so he perscribed me a few doses of prednisone, and told me to take zyrtec in the mornings, and benadryl at night along with 2 puffs of an inhaler every 4 hourse and I have to use advair once Im done with the prednisone. Now what I want to know, Is it really safe taking all of this at once?