Thank you for your query.
I understand your concern but you have not provided the complete details of the investigations like the total and differential counts. Platelet count
of 645... is incomplete for me to say if the count is low.
There can be a number of reasons for headache and if the sinuses
are normal radiologically then I think that you can wait and observe.
I hope I have answered your query to your satisfaction.
Wishing your son all the best.