greetings,
motivation, procrastination and concentration are all facets of the a similar coin though the real question is what are you trying to accomplish.
i have been working on one game for almost as long as you have, when i started i was told by more than one person no one had ever figured out how to do it and not for want of trying. it took me years, especially to optimize it, get the AI working, its not easy, but hard work is not about you or me, it is the game itself, like a book or a painting or an idea it must stand alone if it is to endure.
i could go on for a great deal of time about this but this concept of sunyata in part, focusing on a single desire and using it as a spoon to empty yourself into an idea until there is nothing left but an empty shell that is the real you and a world you have created from the contents of what you thought you knew, it is painful and terrifying but at the same time beyond words in beauty, even more so when you realize that your hard work is ultimately just as meaningful before you ever began and it could be reduced to dust and it would not matter, the majesty was always there to begin with.
meditation would be good for you, just dont think sitting there and humming about peace and love is good enough, if you are not willing to examine yourself, especially your contradictions and darker aspects then your not doing it right.
aside from that i could recommend a number of things but they heavily depend on both your physical state and proclivities.
dark chocolate, exspecially with all the cacao oil, is something you can almost never go wrong with especially of its a cultivar with little or no caffeine and lots of theobromine, changing your diet, eating more fish and greens, some forms of exercise would be very helpful if your problem is your body or mind becomes weary. also you might want to look into nootropic stacks especially in reguard to the racetam and ampakine classes.
if you are taking any drugs, even if they appear as minor as aspirin or given by a doctor or are something else entirely, you should take the time to thoroughly understand everything going into your body and how it effects you, you would be amazed how many of these things can have long lasting effects on how your brain works even after they have cleared your system. some things are very useful and when you are sick can be absolutely essential others can cause a huge detriment and you need to understand what is going into your body.
never underestimate sleep.
but assuming there is nothing physically that is off setting you (and that alone can take weeks to address) it still comes down to you being willing and finding motivation, in my experience, is normally a problem with choice itself.
you have to address what ever it is you are choosing to do other than work because no matter what you think you want to do you are choosing to do something else, this might sound somewhat mundane but the crux of this is rather critical: until you understand and address these choices there is only so much you can do because the things you want will cause you pain if they are not relinquished. its not like you have to throw those monkeys jumping around on your back off, sometimes they can be very useful, but you do have to get them to settle down or redirect them towards being helpful rather than hindering you because ultimately they are trying to help and often times the choices your making that arnt what you want are still very valid, you have to acknowledge them in order to get them to settle down.
so yeah, consider looking into learning how to do real meditation, it wont be easy but its the fastest and most through was to address your impulses and choices that i know of.
good luck.
