Bad rash on chest that won’t go

I suffer alkergic asthma in the spring, so told to continuously take anti histamine.my GO

told me to stop taking them now for a break. I came out in a very ugly red blistered rash across my chest and up my neck. My GP said it was probably just coincidence, but after 3 weeks it is still driving me nuts. Does anyone take anti histamine continuously or must I always have this ugly itchy rash. Many thanks.