My 13 Year Old Daughter Has Had Approximately A 99

My 13 year old daughter has had approximately a 99 fever, sore throat, sore ears since Thursday. She was tested yesterday for strep and influenza A yesterday and was negative. She is now telling me she has diarrhea. Could one of these tests been wrong? The pharmacist said as long as the fever is low grade OK to take Imodium. How long do I give the diarrhea to clear up before going back to doctor?