Why am I doing this to myself?

Because you think you deserve it. Because you think you don't deserve the good things. Because you love "too much." Because you have a tendency to ruin yourself. Because you have problems. Because you have so much emotional baggage. Because you feel alone. Because you feel unworthy. Because you feel lost. Whatever it is you're doing to yourself, you need to know that it can change. It won't become a cycle (anymore) if you don't allow it to be. You are worth so much more.

your doing this to your self because thats your way of coping with whatever is going on in your life.

We often talk to and treat ourselves in a way that we would never treat another person. For example, you would never tell another person they are useless, yet you may find that you tell yourself that exact thing. Try to treat yourself the way you would treat another person, you are one after all.

Because you forget that you value exactly as everyone else never less. You tend to keep a lot in that to cope with the intense emotional pressure, you distract your mind with physical pain which sadly becomes a relief and distraction, an escape of reality and sometimes addiction. Because you think you deserve it and suddenly the self punishment process feels good and as if it is what should be done. Loneliness, feeling unworthy, never able to measure up to some expectations, useless, unheard, mistreated, feeling in a chaos not knowing which way to go or what to do with nobody there to help you. A lot of unexpressed emotions and bad thoughts keep battling and racing in your mind that the only way to make it stop is a strong distraction, often inducing physical pain or harm. I'm sorry if you're experiencing this, it can turn to a vicious cycle. And know you value exactly as everyone else, you matter, you are loved, you are born for a purpose and you never have to suffer alone. You deserve better!

You feel unworthy, like you deserve it. You want to expose how you feel somehow, and might not know how.

I think it's because it is a reliever of some kind. Something that feels good after the deed, what ever it may be, is done.