I recently listened to a show on Public Radio regarding memory and the best ways to learn new things. They said some studies have found that memorizing by repetition is not very efficient. They found that being tested on what you are supposed to learn greatly improved memory retention. The more you are tested, the more you remember.
You might want to divide your studies into "lessons". Before starting a lesson make a short outline (3 or 4 items) of what you expect to learn in that lesson. As you go through the lesson try to come up with positions or questions you're supposed to be able to solve after the lesson. Then, after the lesson, try to solve those problems/questions. I think it would be a good idea at the end of each lesson to also try solve the problems from the previous two or three lessons. That way you'll be tested several times on the same material.
1) Many top players are known to have excellent memories.
2) If you forget something, look at it again.
3) If you forget the content of a text shortly after finishing reading it, it probably means that you should read less of it in one go to get something out of it.