I disagree with some of the posts in here. The problem *IS* marijuana.

He is not saying that he can't motivate himself. He is saying that the short term memory loss is affecting his studies. I know for a fact exactly what he is talking about. I bet ALOK can concur. Have you ever been studying and realized that all you are doing is staring at the book and thinking about something else?

I too leave my apt unlocked, leave my headlights on (had to jump it 3 times in the past month), lose my keys and generally accidentally do stupid shit.
If you continue to smoke daily, after about 6 months, it will become less apparent and you will be able to study and function. I think the 'stop and start' trend is what is fucking you up. My worst problems arose while I was doing the same thing...a regular but not daily smoker.

Either get on the train or stay off. Its the side effects of marijuana that are causing you to lose your concentration. If you don't want to quit, maybe try to find a different strain that doesn't do you like that. Some pot i've smoked will literally give me a 15 second attention span in which I cannot get anything done. Others I can focus on one thing for a long time and gives a 'clear' high.