My Daughter Has Been Fighting A Sore Throat For 2

My daughter has been fighting a sore throat for 2 weeks has been to a cvs minute clinic 2 times (yesterday), she has been tested for strep 2 times and both negative, now today she feels really crappy a very bad sore throat and can barely swallow. She has a low grade fever of 99.9 temperature. What do I do now? She has been gargling with salt water and taking ibuprofen. Do I make another appointment with her primary doctor ?Could she have Mono?