I Stress About Stress Before There Is Stress To Stress About

So, I am practically a full-time student, work over 20 hours a week, and on the other days, I go to church. My friends don't understand why I am stressed. They just say "manage your time better. It's not hard." And it pisses me off. I need down time, too. Do I have a right to be a little pissed about that? Sorry this isn't really a story, I'm just honestly looking for an honest answer.