Hello, Thank you for your question. Pharyngitis (throat infection) can be caused by bacteria, virus, fungi or sometimes caused by non-infectious type like mechanical or chemical cause. By your description it is clear that you are definitely suffering with an infectious type as your son also suffering from pharyngitis. Usually the white spots are the exudate of the infectious organism. This is most commonly seen in bacterial infection. But it can also be due to a viral infection as you had negative strep test. The diagnosis is usually based on the symptoms and as well the culture test. Once you get the culture done can start the treatment according to the organism either antibiotics for the bacterial or NSAIDS. Please do not hesitate to contact for further information if needed. Thank you Dr. Shailaja