Hello. I am glad you contacted me for your problem. Sulfamethoxazole is a Sulphur containing drug. People can be allergic to drugs containing Sulphur. The symptoms of wheals that you mentioned do fall into the category of an allergic reaction which most probably are due to the drug intake, if they did start after starting the drug. The thing that I am more concerned about are not the wheals but the low blood pressure that you have been having lately. This symptom shows that you might have or are going towards a major allergic reaction. The first thing I would like you to do is to STOP taking sulphamethoxazole immediately and if you have access to an over the counter anti-allergic like Benadryl, then take a dose of the anti-allergic medicine as early as possible. Take lots of water to keep yourself hydrated and flush the drug out of your body and get medical help by going to the closest emergency room or doctor. If your symptoms do improve by stopping the drug then you will need to remember the drug and do inform doctors about this event when next time you ever get prescribed any medication. I wish you the best and hope that you recover soon.