I have been having flu for 2 weeks. my head is pounding and feels like my skull is exploding. i would like to know if l am having sinus infection?

Sounds like it: The "flu" typically runs it's course in about 7-10 days. If you are having cold-like/flu-like symptoms beyound that time (without body aches)... It is likely a sinus infection. Symptoms you would expect: nasal stuffiness, facial pain/pressure, tooth pain, ear pain, throat pain, fatigue, headache.. All symptoms of sinusitis... See your primary care for further evaluation.

2 Week Flu: The flu does not last two weeks. A typical course is over by ten days. The "2 week flu" has now become something else, likely a sinus infection. Go see your doctor. Sounds like time for an antibiotic.