I Had A Doctor Visit Me At Home Due To

I had a doctor visit me at home due to having a servere rash and welps. He described me predisolone. He gave me 2 tablets last night and a perscription to take two tablets once daily with food for the next 2 days.
When i spoke to the chemist he said I should be taking another 2 tablets for today. By the time I finish these tablets I would have taken 3 days dosage. Is that safe. Also I always thought when you have a rash that you should have a antihistamine.