Have you ever been assessed for Attention Deficit Disorder? My stepmother and a close friend of mine were recently diagnosed and have since been successfully treated for adult ADD.
I hope you find a solution.
You could be drinking too much caffeine. Try not having any, see if it helps.
You could not be eating foods that can calm you, like vegetables and whole grains.
You could have ADD as suggested above.
You could have bipolar - which sometimes is misdiagnosed for ADD and vise versa. Bipolar can make your mind race, as well as make you depressed.
I am 19 years old, I don't drink caffeine too much I tend to stick to low sugar juices and waters. I only eat whole wheat bread and noodles, I eat fruit more than vegtables, so maybe that's affecting it? But never really thought about bipolar...