Hello, I am concerned about my 5 year old. He has been sick since Wednesday. Fever, chills, nausea, some vomiting, headache, muscle aches, nasal congestion. We took him to the doctor and they tested for type A and B flu and it was negative. He is still experiencing fever, nausea, and nasal congestion. Should I take him back to the doctor since he has had a fever for 6 days ?