I was on Bactrim for 6 days until a severe allergy reaction break out on me. I was sent to ER and I stopped taking it, then all allergy reaction went away in 5 days but the rash returned after a week, Now I have itchy rashes all over my body, my doctor gave me an allergy shot and I have been taking antihistamine for about 3 days now. My questions are 1) is it normal for drug allergy to return after it went away?
2) how long will Bactrim stay in my system ? 3) how long will it takes for rashes to go away ?

Thank you