I am an organ transplant recipient. i woke up this morning with a sore throat, severe diarrhea and a headache, but no fever. is this a mild flu?

No. No, no no!!: You as a transplant recipient have a responsibility to adhere to your doctor's recommendations, and this would include calling your transplant center when you are sick, not getting answers on the internet. Call your transplant doctor(s) or their nurse(s), and let them know your symptoms so they can decide whether you need to be seen urgently or if this can wait.