Sulfamethoxazole-trimethoprim Muscle Cramps, Pain Killers, Arms and Legs, Couple Minutes, Sweatpants

So I took one pill at around 10am and a couple minutes later, I felt a headache coming on so I took a 1 hr nap. When I woke up, my head is throbbing and my eyes were bloodshot. About another hour later, I was shivering. I had a sweater an sweatpants on, 2 blankets and a heater and was still shivering. The headache was worse and I had a slight fever. Later I felt numbness on my fingers which later turned into muscle cramps all over my arms and legs. I had to position them a certain way just so the pain could be bearable. I took several pain killers and none worked. By 8pm, the pain was just horrible. I couldn't fall asleep, I was just hurting everywhere. The next morning at around 6am, I took more painkillers and this time they started working and I fell asleep. I woke up at 10am and the pain was gone. My eyes are still bloodshot but my body no longer hurts. It literally took 24 hrs for the side effects to wear off. I just can't understand how one pill can do this to someone and still have it on the market!