I sometimes get a a sharp pain like that when doing heavy squats or leg press, or when I'm really hittin my abs hard it's deeper in the muscle of where I have an old scar from an appendix surgery stings like needles being poked in my muscle!! I always figured it was the scar tissue stretching/tearing slightly!!
a tear in your lower abdominal tissue is a hernia and that sounds like maybe what's goin on... however it may not be to serious yet, lay off the exercises where you feel it and see how it goes... might clear up... then ease back into your routine, if it persists go have it checked!! or if you have insurance... go get it checked!!