I feel this post so much it's crazy.
I can can totally understand the emotional roller coaster. Constantly switching back and forth from being totally motivated and driven to do something, then later that day you're just out of it and depressed with no desire to do anything.
I dont know know too much on the diet specificities that everyone has posted above. I've removed dairy and oats completely, but I don't think much has changed physchologically. And I'm sure there's tons of ways to help improve your state of mind with natural foods and vitamins. But some people (like us) are simply just cursed with a hyperactive mind.
I try and do my best to understand that everything I feel is just my emotions. I realize that they are just my mind interpreting what's around me and aren't exactly real, but I also don't just blow them off like they're worthless. We feel them for a reason. So I try and ride them out. I'll go to the gym when I'm super angry and take advantage of that energy. When I'm sad I play guitar, when I'm stressed out and frustrated beyond belief I blast music in my room and dance/sing it out. Kinda weird, kinda different, but I'm learning to control this hell of a ride my mind puts me through every day. It's hard, but I'm making progress. You can too. Take time to learn yourself. What makes you happy? What makes you sad? How can you take advantage of these emotions to benefit yourself.
Try new things, and never, ever, beat yourself up about the way you feel. You feel that way for a reason. Enjoy your emotions, they can be fun. And most importantly, you're only human, it's okay to be a little crazy.