THis website has been a tremendous help for me. Two days after I was prescribed 500 mgs of Bactrim twice daily, I started feeling really odd. First the achiness, then my left leg began to swell. I am not taking the meds anymore, but am now so fatigued, and sore, I feel as though I have had the flu for a week. I honestly do believe that it also has a negative effect on the liver. Just from the almost constant ache , I have on my right side. I just want to sleep all the time. I have not taken the meds for two days, and yet, the effects remain. Beware of this nasty medication. I don't know why the FDA allows its distribution!!