Hi Milena! I felt just like you when I prepared for the CAE. I suggest using the Advanced Language Practice by Michael Vince, and if you think it's too advanced, you can always go to First Language Practice by the same author. The books are divided into two main sections, one is for grammar and the second part is for vocabulary. The grammar section is very clear, with simple explanations. The vocabulary section is grouped into topics or main areas.

I highly recommend using this book, I used it over twenty years ago, and I use it with my students (I'm an English teacher), it has been revised, of course!

It will surely help you to improve your vocabulary and reinforce your grammar.

Good luck!