HI, thanks for using healthcare magic
If he has a history of
sinusitis and the sinuses were painful then it is possible that the headache is related to congestions of the sinuses. This is one of the possible causes for headaches.
He may want to consider the use of an oral and topical decongestant to reduce the congestion. This can be used along with a
topical steroid nasal spray, mucolytics to reduce the viscosity of the mucus and warm compresses applied to the fact to encourage drainage.
An anti inflammatory pain killer such as aspirin, ibuprofen,
diclofenac can also be used, these should be taken on a full stomach.
Decongestants and mucolytics should be available over the counter.
Intense pain can sometimes be associated with nausea.
It is unlikely to be related to a gastrointestinal virus because his symptoms would be mainly
abdominal pain or cramping, nausea, vomiting and diarrhea.
I hope this helps