Suggest Remedy For Rashes On The Legs

I am 50 years old. I take Toprol and amlodipine. Recently i.e. this has happend three times. After working in the yard, cutting grass, weed eating, my legs break out in a rash. It's splotchy patch and burns. I put cortizone cream and in a few days it gone. Recently I walk through a botanical garden and the next day it was worse than ever covering my legs even where clothes were covering my skin. In all cases I was exposed to the sun for several hours wearing shorts. I have never had this problem before starting heart medication three years ago and this year is the first year of the alergic reaction or rash? Is it my medicine?