Thank you for your query
His headache can be explained with the sinusitis
. With due course of antibiotics it should resolve. Try giving him some steam inhalation. It is very helpful and also relieves the headache. The stomachache can either be a gastritis
or a colic
. If is is gastritis it should respond well to antacids. Please don't give his medications empty stomach. Try some probiotics like curd. Else he may require an antispasmodic. You need to consult your doctor to get one of those prescribed.
Hope this helps. God bless you!!