GMAT scores keeps dropping - What am I doing wrong?

Hi Guys,

I feel very stuck in my GMAT preparation and is unsure how to move forward, any advice and suggestions would be very appreciated!
I started my GMAT preparation in July and had my first gmat test in October (I realised later that I was preparing in the wrong way by starting off with OG questions.) Anyways I did the exam and got 640. (Q43, V35) October 29

After the first exam I bought the Economist GMAT tutor and studied the GMAT full time. The following are the scores of my practice tests prior to my second exam:
1: The economist practice test, got 710 (Q45, V42) December 2nd
2: GMAT Prep practice test 1, got 700 (Q46, V40) December 6th
3: The economist practice test, 760 (Q50, V44) December 8th
4: The Economist practice test, and got 720 (Q49, V40) December 12th
5: GMAT PREP practice test 2, got 680 (Q48, V34) December 14th (was very tired and sick)

I felt very good in my GMAT preparation, and felt confident with all the content. So I took my second GMAT exam on the 18th of December, I think I had a serious case of exam anxiety and underperformed, gotten a disappointing score of 650 (Q49, V31).

I booked a new test in January immediately after the exam. But now every time I do a practice test the score just keeps getting lower and lower, especially the verbal section.
6: GMAT PREP practice test 3, got 670 (Q48, V33) December 26
7: Then my last practice test today: The Economist practice test 660 (Q48, V32)

I have been trying everything I can think of to get my Verbal back up again, doing questions in advanced questions OG, doing questions on GMAT CLUB, but it just keeps going down. I am very very discouraged and feel hopelessly confused on what I'm doing wrong. Please give me some advice on how to precede and what to do this last week before the exam. (My last chance before application). Any suggestion is greatly appreciated.

Thanks!
Melissa