Sulfamethoxazole and strep throat

I have been taking the med for about one week and things have gotten worse each day. I searched on the internet and found this website yesterday. I was experiencing extreme pain in my head, neck, and back. I was developing a red rash on my legs as well. It hurt to open my mouth or breathe and my throat felt like strep throat. I decided to go to the ER due to bizarre symptoms. It was a little similar to a really bad sinus infection. The Dr. checked everything and said I was completely healthy and had no infections in my body. He said he could not explain the fever and was concerned that it may be an exotic illness or a reaction to the medication. I quit taking the med and I am feelings much better. Why do people prescribe this terrible med, when there are so many other options for antibiotics?