Yeah. Everyone has a subject they suck at, or more than one. With millions of pursuits in this world, we're bound to do poorly at most of them, whether nature or nurture.
I didn't get my bachelor's until I was 32. I received my associate's when I was 25, then went to work for a vending company for the next five years until I was in a major auto accident. Workman's compensation paid for a year of college after that, and I gutted through the last year. Now however, I have full health care, a retirement plan, paid vacations, and a career I care about...it was all worth it in the end.
The thing was, I could have had that bachelor's degree when I was 22. I had scholarship opportunities that I turned down. After high school, I wanted to get out and earn some money, so I turned down (!) free money for school so I could earn some for my personal desires. I was a smart kid, but not very practical. In reality, I could have had real money ten years earlier if I had just gone to college right away, when my opportunity knocked. It was ten years later--and a hundred times more difficult--when I finally got it.
Focus on the benefits and rewards of your education, if that helps to get you through. Or listen to more stories like mine and Mathim's. Wherever you get your motivation, get it. I've read too many studies that say motivation is the most important factor to success in life, and I agree 100%. It isn't always the best or brightest who succeed--and I'm neither--it's those who never give up.