You and I are very similar. I wouldn't say that I've got ADD, but I did fall into depression while in college, and have the same difficulty with managing any kind of long-term work or commitment. It also affects my personal finances; unless I set up automatic transfers to saving accounts, I am unable to keep anything for more than week or so.
So I ditched college at 20, was lucky enough to get a good job despite that and work from there, but as I slowly get closer to 30, I find that the world has less tolerance for my problem. I'm moving up in my professional life, and as I do I find that juggling with long term projects is starting to become more and more important to my work.
But anyway, you wanted help or advice.
One of the ways I am coping with it, is trying to make sure I can capture motivation when it happens. I guess my issue is not that I have NO motivation, but more that I am unable to summon it myself. But it happens to pop up at times, so I found that I can get things done if I remove obstacles that would stop me from using it.
For instance: I am trying to learn how to draw these days. It's a skill I always wanted to have and I decided to fix that. But most of the times, I don't feel like doing it. Just because I have free time doesn't mean I'm able to force myself to draw. So I always carry a sketchpad and pencils; whenever the motivation to draw crops up, I can catch it and make use of it.
Another example: I'm taking classes on Coursera. Sometimes I feel like listening to the lectures and doing the class work, sometimes I don't, and I can't really force myself to do it when I don't want to. However, since Coursera works well on my cell phone, I am capable of listening to the lectures anywhere at anytime.
Never underestimate the small stuff like doing the dishes. In my case, two things I would like to do is put some money aside and lose some weight. As ridiculous as it sounds, making sure I deal appropriately with the dishes is crucial to attaining these goals. Why? One of the biggest reasons I can't save money and that I am getting fatter is because I am always eating takeout or delivery. It is both expensive, and unhealthy. I would really like to cook more; I love cooking. But as I said before, you need to remove any obstacles beforehand if you want to be able to capture the motivation when it happens. Having to do the dishes before cooking is such an obstacle. Having to go to the grocery store is an obstacle to cooking. So something as small as a dishes problem, is stopping me from dealing with my cooking problem, which is stopping me from dealing with my money and health problems.
I try to have many hobbies going at once; the more things I have that I could be doing, the more likely that there'll be at least one of those things I'll be wanting to do in my free time.
I also try to keep the work divided in smaller chunks and set small, tiny goals for myself. For instance, like yours probably is, my room is a stupid mess. Worse than a messy teenager's. I would never be able to tackle clearing ALL of it; it's waaaaay beyond any motivation I can muster. But at some point I wanted to use my desk. So when the motivation came up for it, I cleaned up the clutter on desk. Same thing with the laundry; one load at a time. My room is still a stupid mess, but at least there's a few parts of it I'm keeping clean.
That's another tip: keep things clean, clear and done as you go. Never rely on future you, that dude will disappoint you. Most people are able to leave things get a little messy, then clean up for an hour or so and are done with it. You are not. You need make a habit of doing things immediately, on the spot. For instance; do the dishes immediately after eating: all of them, always, even if you have guests. If you let them pile up, no matter how small the pile, that will be one pile you will never really want to deal with until it becomes a problem.
Anyway, good luck. I'm rooting for you.