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Headache after sinus infections may last for long periods as collection of mucous occurs in sinuses
especially frontal or ethmoid sinus
. But sinus pain is typical in that its a dull pain mainly in frontal and temporal region, it usually start in morning, that's why it is also called as office headache.
Most of the investigations in such pain come normal.
Still to be on safer side go for MR scan as it can easily detect even slight Haziness in sinuses.
Second steam inhalation for 2-3 times a day will prove useful as it will liquefy the secretions and will help in quick drainage
. To have symptomatic relief take antihistaminic medicines for at least 3-4 weeks. Paracetamol
for SOS basis can be used for headache.
If you don't get any relief with this then go for Sleep Study.
Hope I cleared your doubt