Do you know why you are thinking these crazy things about yourself? Nobody on this earth is worthless, we are all here for a reason and God didn't make anyone worthless. You know you are moody and you are right there, that nobody wants to be around someone who is moody, it will be a sure way of killing friendships.
You say you know you need help to deal with traumatic things that have happened to you in the past, then go and speak to your doctor, that would be a good starting point. Ask him to refer you to a counsellor and then you will be on the right track to finding out the answers to the questions you have.
I wish you good luck and I hope also that you will continue to post and let us know how you are going.