maybe it never went away? you can be a strep carrier and always test positive. next time have a culture after you have been properly treated and see if it is gone. if you are not a strep carrier you may be getting exposed from someone who is. frequent strep infections or a strep carrier state may justify having tonsils removed since tonsils are usually the reservoir for this bacteria.
why do i keep getting strep throat? . for the past year i have been diagnosed with strep throat eight (<positive_smiley> times. why has it been recurring so often?