I can pretty much draw anything from reference but why cant i draw anything from memory or imagination? how can i learn to do this? no matter how many times i draw the same thing i can never do it without reference.

I have the same problem :D If I get a picture on a comptuer, I can draw it almost perfectly on a piece of paper. But as soon as I go, "I should draw this." And I don't have anything to look at, it's just like...blehh!

simply practice a single topic over and over again. for an example, human bodies. once you practiced drawing human bodies and shapes for a while, you'll gain a better understanding of the human body, allowing you to draw a human figure right off the bat. so i think it impossible to draw something purely from memory. you need repeated encounters with the topic. and the imagination part in the other hand is more like your own design. purely of your imagination. this happens to me too while i draw. it sometime gets pretty annoying when you try to draw it again. lol..