Error Log is a powerful tool, as it allows you to specifically identify which types of questions you answer incorrectly. It's much easier and faster to improve your performance this way, as it allows you to focus on your weaknesses.
But I suspect that your problem centers on fundamentals. The best book for CR is
Powerscore CR, while the best for SC is Manhattan SC. If you're first language is not English, then I strongly recommend those two guides. Other, general guides simply will not suffice. Another possibility is to read some
GMAT Fiction whenever you have the chance. This is a relatively pleasant way to become more comfortable with reading in English.
The
OG should be used for practicing and determining whether you have absorbed the necessary concepts previously learned. In other words, the
OG must come after the study guides. Do
NOT use the
OG as a substitute for learning those concepts.
But, if possible, could you tell us a little more about your study schedule? Maybe some of our responses are not directly relevant to your particular situation. The more information we have, the better advice we can offer.
In the meantime, if you haven't already done so, make sure to check out this link too:
best-gmat-verbal-prep-books-reviews-recommendations-78094.html?highlight=ml308