I think comparing yourself to people taking x credits is futile and bound to be depressing. I mean, they're different people with different skills and stresses. They could be taking really easy classes, or have no social life, or require less sleep than you. And it doesn't matter. What matters is balancing your life for yourself.

In the long run, getting all As is completely useless. Frankly, I wish I'd had more fun in high school and got more Bs. It took me until grad school to figure this out, though (and I didn't get anywhere near all As in college, ha! I just angsted more). It's better to figure out the school-work-life balance in undergrad. And a lot of that is not beating yourself up about grades (easier said than done).