Anyone advice? Went from 630 to 470!!!

I’ve been planning to apply to a Masters in Finance in US since the middle of last year but I am quite desperate and confused with my GMAT. A little bit of my background: I am 24 years old, graduated 2 years ago with a degree in Business administration in São Paulo and I currently work as a junior trader in a Brazilian Hedge Fund.
I started to study for Toefl first and I had struggled to get the required score. But by the end of the year with many hours of study I was able to reach the minimum score. This gave me 3 months to study for the GMAT and apply to the schools that I wanted. The mean score for the schools is about 700. I planned to take 2 tests in case I didn’t do well in one of them and I would use the other result for my application. I studied two months and I have taken many practice tests (maybe this was a weak point of my prep).

1. 21/11 41Q 21V - 530 - GmatPrep 1
2. 27/11 42Q 31V - 590 - MGMAT 1
3. 3/12 45Q 30V - 610 - MGMAT 2
4. 4/12 43Q 32V - 620 - MGMAT 3
5. 7/12 44Q 35V - 650 - MGMAT 4
6. 10/12 44Q 35V - 650 MGMAT 5
7. 11/12 44Q 37V - 670 MGMAT 6
8. 17/12 40Q 26V - 590 Kaplan Free Online Test
9. 18/12 570 - GmatPrep 2
10. 18/12 31Q 25V - 530 Kaplan 1

As you can see my scores were quite confusing. But after I researched I saw that this is not that uncommon, some people have very different results on gmatprep and mgmat. And by the end of December 2011 my Gmat score was 630, 49Q 27V. I was quite satisfied, because my goal for this first test was 650 and the second was 700. So I kept studying as I had been doing. I used an error tracker and used the theory books as I saw the need for theory basis. And now stranger things started to happen with my GMAT CAT scores:

11. 14/01 47Q 33V - 660 - MGMAT 1
12. 15/01 39Q 28V - 570 - GmatPrep 1
13. 18/01 43Q 34V - 640 - MGMAT 2
14. 21/01 45Q 32V - 630 - MGMAT 3
15. 22/01 43Q 23V - 550 - GmatPrep 2
16. 25/01 41Q 29V - 580 - MGMAT 4

I tried to find on the forum a similar case as mine but I didn’t. Some people see some decrease in their scores but it shouldn’t be so drastic. Mgmat for example was a 90 points difference. I got a little bit disappointed but as the first GMAT that I took I knew that I shouldn’t rely as much on these scores. And then yesterday was D-day: 470, 39V 16V. I couldn’t believe what I saw on the screen. I knew that I didn’t do that well but this was not in my plan. I felt this was like a punch to my stomach.

Now I have no idea what I should do. The deadlines for my schools are 15th February. I will try to call them on Monday to see if they will allow me to take another test in one month. If they allow me I also have no idea how I will study for the GMAT. If they don’t allow me how should I study? Take one pre-designed course such as knewton or a private tutor? I feel lost and I would ask for some of you to give me some guidance of what I should do for now.

You can't necessarily use practice test scores as a predictor of your test score on the actual exam. The exam is a CAT so if your psychology and timing are off, and you get answers wrong in the very beginning, your score is immediately going downward.

If you've taken so many practice tests before, did you take them casually? or under timed conditions? If you have no clear attack strategy, on exam day you're going to panic a little bit more than usual and that is going to affect your score. Always study/prepare with a few questions, then when you take mini-quizzes or sit for a timed test, you really have to simulate it. And of course, develop an attack strategy. Figure out what that should be.

Thanks for your response. All the tests that I took were timed. This was a big concern for me because during my first tests I always had to guess the last 6-5 questions. On my first Gmat I had this problem with Verbal, I guessed 2. The same thing for the last Gmat that I done.
Yes, I've been doing sets, always giving the focus on timing.
Maybe timing shouldn't be my major problem. My concern was that after my first Gmat my scores were decreasing consistently. And the weirdest thing is that during the practice sets I noticed a big improvement, especially on verbal, which is my weakest point.

Best of luck on the retake!