Are you sure you've truly DONE the problems? Remember that studying is not simply running through, doing the problems, checking the answers, and moving on. For every problem, you should be able to:
Explain how to do it in at least two ways,
Recognize the problem type you're dealing with,
Create a similar problem with slightly different facts and/or numbers
Get some sort of "takeaway" lesson that can be applied to other problems
Explain the problem to someone who has never heard of the GMAT before
Solve it again tomorrow in under a minute
It's through this analysis that you will learn more and get into the high 40s. Personally, I only studied from the OG and truly believe that if you understand every problem in there, you'll get an amazing math score.
Also, have you purchased the supplements to the OG? That will give you a few hundred more questions.
Jim S. | GMAT Instructor | Veritas Prep