I have been working through the practice questions in the SAT blue book, but I don't feel like I am making any progress. How many SAT practice tests does it take to see an improvement in my score and how many tests should I take before the March 5th SAT?
The truth is that the answer to this question is highly dependent on your starting score and how much you hope to improve. It also depends on how thorough you are about reviewing your mistakes on practice tests.
If we're just talking about the March 5th SAT, you have five weeks until the test. In that time, I'd recommend taking around 3-5 full practice tests if you want to make significant improvements. After each test, make sure you go through your answers and keep a record of which questions you got wrong. Then, spend a few hours reviewing the areas where you had trouble and practicing similar questions before you take another test.
If you plan on taking the test again and will be doing more studying, I would say taking one full practice test every two weeks or so is a good rule to follow. Don't just take practice tests one after another and expect to see improvements. This type of practice can only get you so far if you don't do the additional legwork of delving into specific issues you have on each section. It's possible that you're not seeing improvements because you aren't spending enough time on this type of analysis.
Here's a helpful 20-hour prep guide that will walk you through using SAT practice tests effectively (you can always repeat the steps and spend more than 20 hours studying if you have time!).