Is It Safe To Use Bactrim For Cellulitis?

For the past 5weeks my skin has been breaking out with first looks like a mosquito bite. Then they turn red swollen hot itchy and leave a scar. They occur about every 7 days but now it seems lately they popping up earlier. My doctor said it was cellulitis and gave me bactrim even on that I m still have having breakouts. Recently have become ill where I m barely eaten or drinking fatigue sometimes light headed