What to do if i have a really sharp pain in my lower stomach right below my belly button. what could this be?

Belly-button pain: Belly-button (umbilical) pain may originate locally due to infection or herniation, or be "referred" from another abdominal location like the appendix. Signs/symptoms of concern include: local redness &drainage, umbilical bulging that can't be reduced with gentle pressure, fever, vomiting, change in bowels, generalized abdominal tenderness (suggests peritonitis), worsening or progressive pain.