There are two main reasons for this (in my mind at least):
1) I haven't been fully immersed in Polish; it's too easy to speak English instead.
2) I don't understand English grammar.
If you have an analytical mind, I think point 2 is very important. The amount of textbooks I've read and failed to understand because it's like they're written in a different language. I think it's a bit like when discussing programming terms with a non-techie.
Anyway, I'm now spending my time learning about nouns, adjectives, verbs and what object and subject are in relation to a sentence.
It's a crying shame that I've got to the age of 28 without knowing this stuff, and a damning indictment of the English educational system (and myself!) /but/ I think it'll be worth it ;)