Could some people shared some of your successful languages learning techniques? For example, how long do you spend on one subject? How fast does it take you to finish a tree?
What works well varies from person to person. I like a mix or learning new things and reviewing existing stuff. If I find I am feeling lost and I can't remember things in the exercises that are from previous lessons I go back and spend a while (maybe a week) mostly reviewing old lessons.
I think it took me around six months to finish my French tree. Obviously certain people can finish a tree extremely quickly. However the goal is not to finish the tree but to build a good foundation for learning the language so it takes as long as it takes.
I know you posted this long ago, but I have tried a new technique this time and it has really helped me. What I do is that i start by learning a skill, then I strengthen (everything, not just the single skill) for about a week. Then I learn a skill again, and continue. I think strengthening is especially important in Polish to recall the correct case endings when you need them.