Headache and dullness to some extent can be seen in virus.
Since blood work up and examination findings would have been normal, you doctor would have felt its just a virus.
Since you say there is no improvement- its better to have her seen by the doctor again.
I wish to know if blood sugar was done? If she is not eating anything- it might add on to her dullness. In such a case she might need to be hospitalized and treated.
Its better you have her seen by the doctor again- get her examined thoroughly- including Blood Pressure, complete nervous system examination, repeat blood as needed.
Blood Tests done before 3 days in any fever
will not be much informative. May be repeat blood will help in finding out the cause.
Hope my answer helps you.
Wish your daughter good health.