My 4 yr old son was diagnosed with flu a a week ago and is now showing signs of what i believe to be a sinus infection. does he need to take any other trip to the doctor or can he be treated at home? hes having eye and tooth pain from time to time?

That would be up to the doctor that treats him. Your assumption may be valid or not and the pain may be from retained fluid rather than a secondary infection. Flu A is well known to irritate the structures of the upper airway.

If he is experiencing facial swelling,fever or green drainage from his nose, he may have a secondary sinus infection. Flu is also associated with congestion, and tends to improve over the course of a week. Keep your son well hydrated, use nasal saline spray and monitor temperature and breathing.