Like yourself, I am an incredibly slow modeler--or maybe I should say overly deliberate. It takes me months to put together a simple kit that a friend of mine can put out in a couple weeks. My problem is that I find myself waiting for one process to finish before I start on another. Of course, other "problems" are family and other, more important issues, that have to be dealt with before I can go back to the bench; but I assume that's not what you are talking about. One thing I am beginning to learn is I have to keep going if I'm going to reach completion. That means gluing wings together while I'm waiting for putty to dry on the fuselage; or putting the turret or gun barrel together while I'm waiting for the hull to dry. Just those small steps have given some quicker completion results. The other thing, I think, is to be obstinately focused, and complete what you start before moving on to something else. Try to establish some sort of personal goal when you think would be a good time to have a model completed by. If you can't see down the road that far, then shoot for a shorter goal. For example, most models are built in sections (road wheels/track, hull, turret and gun). Set a goal for a subassembly, and then the next, and so on; then see the completed model as your final goal.
One important thing to remember, is that this is a hobby; you're supposed to enjoy it. If you're not, then it's time to find another one. Who or what are you building for? If you're not building to please yourself, and see yourself and your creativity expressed in your work, then maybe you need to rethink the why's and whatfor's. I also find a great deal of relaxation in what I do. It helps me escape-for a short period of time-from the cares and demands of the responsibilities placed upon me.
Lastly, it doesn't matter how long it takes, provided you're having fun. I used to get angry at my brother, because he could just about build a kit in one evening, and I hadn't even gotten the first piece cut from the sprue. It turns out he has a great deal more mechanical ability with pieces and parts than I do; he can also "see" better in 3D than I can. I'm too much a two-dimesional type person, but I've recognized that I am who I am, and have learned to appreciate my own abilities and limitations and work within them; you should, too.
In short: Relax, have fun, stay focused on what's at hand, set some short and long-term goals--and remember that a QUALITY build takes time--sometimes lots of it!
Hope this helps.
Gip Winecoff