Hey kiddo...
This is kind of funny. I went googling "I'm depressed for no reason" and a bunch of results were returned, including yours. I'm also down for no reason and really just came out here to feel "not alone," I guess. But then I realized something another friend told me. A reason why people feel "down" is because they don't feel valued. So you have to CREATE that value. So, for example, instead of feeling sorry for yourself, perhaps reach out to help a student who is struggling with their studies (since you're very bright, this should be easy for you to do - don't undermine the fact that you got those
scholarships - dummies don't get these!!), or volunteer at an animal shelter - better yet, adopt a pet and care for it for the rest of its life, visit a nursing home with some friends and sing Christmas carols to the older folks, think of some crap your family or friends are going through and take the initiative to take something off their plate, etc., like run an errand for them, or bake them a cake. Seriously, no one today does anything for anyone anymore, and when someone does, it's a BIG deal! YOU will be their
hero. It'll make them feel good, and it'll make you feel good. A win-win situation. By taking the focus off of you and onto others, you'll see a difference (since its external to you) and those are the kinds of things that will set the wheels in motion. I notice I'm in a better mood after taking care of my cats or doing a favor for someone who shows their appreciation.
Also, keep in mind that the seasons are changing, and sometimes that gets people down. Perhaps you're anxious about the holidays (I know I am - I have had family relations badly damaged over the past few years and it saddens me), or it could be even chemical - Seasonal Affective Disorder (coincidentally, "SAD"). Know that whatever it is, you do have some if not all control how you react to the changes around you. You just have to make the choice to do this.
And look...now, hopefully, I've helped you, and if I did, then that makes ME feel good.
Good luck, and let me know how you're doing.