Thank you for putting your story out there, Misery. I hope it helped you a bit to get it out, and I'm sure that it will help many others who can relate to various parts of it.
I just want to say to you that it is not too late to start taking care of yourself. We've all put our bodies through a lot in some form or fashion, but you are still very young and have a lot of time to enjoy a healthy life. If you look at the years you spend making not-so-great choices as blips in an overall lifetime of generally good ones, you still come out ahead. I commend you for making that decision at a young age. I also want you to know that you deserve this...for many people, feeling that they deserve the time and effort it takes to get healthy is one of the biggest hurdles to get through.
Take one step at a time, make small changes along the way, and challenge yourself and be gentle with yourself when you need to be. You can do this. Use the forums for support, for answers, for opinions, whatever you need. There are a lot of people here willing to share all of the above and more and we are looking forward to seeing more posts from you!
And now that you don't have to be perfect, you can be good.