I know how that goes. I've been kinda down for the past week or so. So I'm gonna give you some advice, and hopefully I'll follow it too :)
Always remember that you are loved. Heavenly Father loves you more than you could ever imagine.
2 Nephi 2:25 "...and men are, that they might have joy"
Remember that one other post? "Hope Always," where I talked about the "depression verses"? Those are especially appropriate when you're in a self-pity mood that you can't shake.
Ya know what else? I read this quote once, I forget who said it, but "talk to yourself as you would to someone you love." That means don't tear yourself apart. Don't beat yourself up. If your friend felt like you do now, how would you cheer them up? Do yourself a favor and treat yourself like a dear friend. You gotta love yourself, cuz you gotta deal with yourself for quite a while :)
Another quote: "Don't give up... Don't you quit. You keep walking. You keep trying. There is help and happiness ahead... You keep your chin up. It will be all right in the end. Trust God and believe in good things to come." -Jeffrey R Holland
And one last quote, cuz I super like quotes "Never let weakness convince you that you lack strength" -Unknown