You are not a good for nothing kid. You are a young man who has yet to discover his gifts and his purpose. I believe one reason so many have reached out to try and help you is because they sense you are a special person. Once again, I can identify with you, when you are in pain, when your life and the things you do have changed because of that pain or illness, you do feel "good for nothing". Feeling that way put me on the brink of suicide just a couple of days ago. Its not true for either one of us, and both of us must find a way to feel we have a purpose right now.
Next time you work, look at your customers. Not one of them is free from problems. Even the "prissy butted rich bitches" (a name for hard to please customers from my Walmart days) can have their problems. Next time you are ready to jump out of your skin from your discomfort, focus on the person you are helping. Make them the most important person in the room. Give that person your best in attitude, courtesy and service. Doing that, one person at a time, will help get your mind off yourself for a little while. Even if you think your manager is a jerk (many are) and your CSM can't find her own rear end with both hands and a flashlight (I was a CSM), treat these people with respect and act in a way that demands they respect you, because you are worthy of respect. Give the best you can and you will be the better man.