I Had The Flu And Been Coughing. This Morning I

I had the flu and been coughing. This morning I was asleep. I woke up with a cough and at the same time I felt a sharp pain about two inches to the right next to belly button. Do you think it is muscular? I can press my hurting area, but no pain, except when I cough. If I press my hand against the pain area when coughing, I don't feel as much pain. The lighter the cough, the lighter the pain. The stronger the cough, the more pain.
What could it be?