I've been having sharp pains in my belly button area when i stretched my torso. i know i'm not pregnant. so what could it be?

Hernia: A common cause of sharp pain in the belly button is an umbilical hernia. You will need to be examined and possibly get an ultrasound. If you get nausea/vomiting and fever with worsening pain, it is urgent and may be appendicitis. Otherwise, for mild intermittent pulling sensation, the cause is varied as many things can irritate the lining of the abdomen. Start with rest and observation.