I really can't say anything that hasn't already been said.
First off, at least you know that there is a problem, and now you have to do something about it. You shouldn't consider your mothers death to be the end of everything and I'm sure you know already know that, yet the feelings are still there. It's completely normal to feel saddened and demoralized, with the death of a parent, even years after they've died.
But quitting on life should never even be an option. You're so young and how do you think your family would feel if they lost you now? You have a whole lot ahead of you, and giving up now would mean missing out on what could be a very productive life.
If you ever see this, I beg you to please consider getting counseling. Even if what I say means little to you, at least know that I would feel absolutely saddened down to the deepest core if I found out that you killed yourself. I'm sure you have many friends from this website you can talk to about this as well if for some reason you don't want counseling.
Please take the support that you're getting from this thread, the emails and the PMs that you've gotten as a good sign. Your family, not to mention a whole community of people here, would never want to see you commit such an act and are ready to help in anyway we can.
I can only hope something that we've said has helped you in some way.