I just took a Sulfamethoxazole/MP DS Tablet and within 15-20 minutes I started having what normally feels like gas pains, except they are all through my rib cage, in my left shoulder and part of the left upper arm. The right arm aches, I ache (like a gas feeling) under my left breast and across the area below the breast area, but above the stomach. The pain is radiating into the lower back and from the back of the neck and up into the head. I took Alka Seltzer, in case it was gas, but it did not help. I took a Nitro under my tongue and it did not help.