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Well I'll tell you that I've been smoking on and off (off and on) for since I was around 12. And my memory is far worse off than my peers today.
I didn't have any motivation to begin with, though, so I can't really comment on the motivational thing.
I would have a guess that you have a perfect memory but that is just a guess so if you will hear me out I shall explain that tapping into your phenomenal memory is only a matter of practicing activating your recall muscle. I bet you can remember how to roll a joint. I bet you can remember what a bong looks like. When you smell weed smoke how do you know that what it is? If you forgot you would be like "wtf is that smell!" every time you toked. Things you remember are stored as senses. Pictures... sounds... feelings etc. Practice enriching your internal world and your memory will wake up. When you go into a dark room and you can't see anything does that mean there is nothing there? Turn on the light and there are shapes colours and objects. Turn on the stereo and there are rich sounds. It's all there you just got to flick the switch.
As for motivation you just have to find out what you really want in life. The people who are highly motivated know exactly what they want and the thought of having it makes them so juiced that they are like a whirlwind in pursuit of their goal.