Male sexuality (as well as female) is extremely complicated. There are many things that make orgasm happen. Anything, physical or mental (as in stress) can keep all the circuits from firing.
You say that the 20 twitches are not really orgasmic contractions so I am thinking those are just the PC muscle twitches common during sex that can really go on indefinitely. They may, however, be those just prior to the orgasmic contractions. I am not sure.
*Do Not* wait 12 days to "store up." It is scientifically proven that any more than 3-4 days between ejaculations produces diminishing returns as far as both semen volume and orgasm intensity as your body will absorb non-ejaculated sperm and semen. Man, certainly a 22 year old man (if that is what your ID refers), is not meant to go that long without ejaculation.
I think there is something to your theory that waiting so long will actually reduce your libido and therefore your ability to easily achieve orgasm as a 22 year old man usually can if there are not other physical or psychological issues. Typically though, this would happen a lot easier to older men.
My advice is to try to enjoy your sessions more instead of just getting off asap. Think of masturbation as more of "self love" than just quick sexual release. Take your time, when you know you won't be disturbed and allow your fantasies to become personal, even vocally. The key is to get as much into yourself (touch every part of your body) and your fantasy (touch every part of hers) to increase your arousal level. Then, with time and practice, those "twitches" will turn into orgasmic contractions again.
I don't know how often you masturbate but, at 22, I think I did almost every day and sometimes twice each day. I would think that your current situation should pass in a week or so. If not, you may wish to consult a physician to see if there is anything physically happening (like low testosterone, etc.)
Keep us informed!