Once again, biochemistry!
I know I'm beating this 'til it's bloody, but if your biochemical situation is not sorted out, you have a hella difficult battle ahead.
As es_mer8 points out, physical and mental activity *helps*. But when I was at my worst years ago, I always felt like sh1t, despite having a real lot going for me (good job, good living situation, hotties who were interested in me, a good social life, etc.). But I p1ssed away most of that with my loopiness.
I tried every sort of positive thinking psychology to turn around, but it was all to no avail. It was like I was "hard-wired" to feel like sh1t.
Then I found out about chronic
Candida albicans "yeast" infection, and how common it is due to overuse of antibiotics, and how that can lead to gut damage, which in turn leads to food allergies, and things started to click. The anti-yeast regimen got rid of chronic diarreah I had for a year straight, and my moods improved. Eliminating allergic foods resulted in a huge turnaround, and cleared out the mental fog I'd been in, and brought a clarity I've never known before.
Only when I finally got to the bottom of my biochemical issues, and straightened things out -- which involved a complete regimen of nutrition, chemical avoidance, anti-allergy diet, exercise, and rest -- did I finally start to *feel* good, despite the fact I had a lot less than before in almost every other respect.
To get out of the hole most rapidly, attack the weakest links first. There's a wealth of information on the net.
You're here, so you're obviously interested in *doing* something about your situation. Leave no stones unturned. There are a million ways to get fvcked up, and the key is to find the right countermeasure. And just what *that* is may surprise you, like it did me.
And do change your screen name.