Sharp pain!! Please help :/?

Once in a while I'll get this sharp pain. Not on my side, more inwards past my hip. Like below my underwear line. It feels like sum one is stabbing me with a knife. It always happens out of no where and it hurts so bad. I hav no idea what it is but it's enough to make me cry. And I hold my breath wen it happens cuz it's so painful. :(