Please help, wanna gain better habits for school?

imma freshamn/sophomore (going to tenth this fall). i dunno why i'm so depressed. i got about a 3.125 this year, i know i have 3 more years but for some reason i keep thinking theres no chance for me gettin into a good college. like, i do very well tests, they always show that i know whats goin on, and alot of times i do even better than the quiet, attentive, cliche smart kid. but i lack motivation to actually do homework, (i often procrastinate, bad habit, i know) and studying. i know i have potential,i i do well when i want to. i wish i could change before the beginning of next year, i really want to get into a good college and succeed. please, i need tips on motivation for studying, doing homework diligentlty, and making more time at home for school.