In some of my private lessons for advanced JLPT N2 students, I noticed that they are not so confident with basic grammar and that might prevent them from speaking Japanese more frequently, though they know advanced grammar.
If you would like to do a review of basic grammar (JLPT N5 and N4) by yourself, 「ひとりでできる 初級日本語文法の復習」is suitable . You can do a review of grammar that you have learned in class, and try good exercises. It might take just 2 months for you to be confident with grammar by this book.
This book is highly recommended for people who have passed JLPT N3 , N4, & N5 and would like to be more confident with grammar.