When I wear pants in lower abdomen I get alot of gas and partly lose stool soon after why?

Needs to be checked. You are 17 and have gas and loose stools.we can not tell you what is causing your symptoms as we do not have enough information. You should have your parents take you to your Doctor to find the cause.we need to know your past history,your diet and eating habits , milk consumption and other symptoms etc,if you drink milk, I will advice you to stop as Milk can cause gas and loose stools.Stop milk. .