El Santo,
It's a shame that you were treated differently than your brother when you were growing up. Sometimes that can create some real head issues. Now that you're an adult, come to terms with your dad's behavior and move on.
About your girl friend, I don't mean to diss her but you may want to have a paternity test to make sure the child she's caring is yours. Once your name is on the birth certificate, you're responsible for raising that child not to mention 20% of your annual income, even it turns out not to be yours biologically. You are a caring and compassionate person, great qualities for a dad. Just be sure the child is yours.
Please make a plan for yourself. You're only 21 and life's been rather crappy thus far. Now it's time for some focus. First, get a full time job. I don't care if it's flipping burgers or whatever, you need a job. That is a start in a resume that can show initiative and dependablilty. (In other words, you work your a## off.) Then decide what it is that matters to you. If it's a GED, then you find a way to make that happen. Also, find resources to help you help yourself. A junior college is a good place to start. Talk to an advisor about how to get a GED. If they can't help you, they certainly should know who can. There are also grants and other resources that might be able to help you financially so you can attend school. If at all possible, acquiring a GED is an excellent start.
Now, you mentioned you can write lyrics. That's great. If it's your passion, something that you really enjoy, then pursue it. If you live in a city that has live music, hang out and talk to musicians. (Stay away from the drugs!) Ask them if they know any song writers and talk to them. Get input from music people. Maybe, just maybe, these life experiences you're going thru need to be in your lyrics.
You say you worked to your best but nothing's come of it. When athletes are in a slump, they get advice from their coaches. You've received a lot of advice from many people on this board who care and want to help you help yourself. And don't forget to look into resources in your community. And remember...Life is a journey, not a destination.