No You don't suck!!!! School is hard and so is life. When I went to school most of my grades were low, but my parents said do your best. Doing your best is all you can do, and try not to stress out about school, these days can be fun at times with youf friends and other classmates, who may also feel the same way you do. I found many people feel the sameway, but just afraid to say it out loud.
Treasure these days, find some kind of sport, or walk or ride a bike to lesson the stress, and think positive about yourself, grades don't always show the real you and how really smart you are.