Bactrim and little red bumps

I started taking Bactrim last Monday evening. When I started to have tightens in the chest and feeling very tired on Thursday evening, I didn't contribute it to the medicine. I went to bed and woke up at 2:30 am because of the chest discomfort. I didn't take my Thursday evening and Friday morning dosages because I felt yucky. By Friday morning, my chest was tight and under my left arm ached. I called my doctor's office and told the receptionist that my chest was hurting and I needed to come in on Monday and that I stopped taking Bactrim. Yes told me that I shouldn't have stopped. So I took another pill on Friday evening. I forgot to take one on Saturday morning because I didn't eat breakfast at home and I didn't take the medicine with me. Started retaking them on Saturday night. Within one to two hours of taking the pill, I started to itch. I still didn't know what was wrong. I finally went to bed and I woke up at 3:30 am itching like crazy. Now I noticed I had red bumps and splotches all over my body (legs, arms, back, stomach, chest, and etc). I have been itching since Saturday night and it is now Monday night. I went to the doctor today and I was told that I should stop taking Bactrim.

I will never take this again.