I can totally understand why you would be frustrated.. I would be too. I think you just need to sit down and ask him what he wants out of life and how he plans to support your baby...Ask him if he wants to work at mc donalds the rest of his life and be living paycheck to paycheck because to be honest with you a ged isnt as good as a high school diploma. It is really good to hear that you are still going and plan on graduating.
I think the only thing you can do is try to have a talk with him, but in the end there isnt much more you can do then that..I mean it is his life. Me personally, id tell him that if he wants to be a good father and be a part of my childs life and he would get up and do something with his life.. He is almost a legal adult and he needs to get his caca together. Sometimes an ultimatiem is the only thing that works.