My first score was 540, and second was 590.
I didn't study much that time so I decided to study more to improve my score for the third try.
After intensive study (I studied at least 4 hrs daily, 8-9 hrs on weekends, and used spare time to improve vocab, too), I was confident I could raise my score.
However, I got
590 again!

I was so shocked! Not a single point up!?
(BTW... only my AWA kept improving.. from 4.5, 5.0, and 5.5 this time)
Can anyone help me???? What was wrong with my study style?
By the way, I am not a native English speaker.
Let me share what I did:
Basics:Studied OG 11 - at least 3 times thoroughly until I understood why I made mistakes.
Studied Kaplan CD over 3 times each
Studied Kaplan and Princeton Review books thoroughly and revisited the questions I missed
Went through PowerPrep (Practice 1 and 2) over and over
Practiced new full-length tests provided by manhattan review and other sites
Quant: Learned the basics again by reading math books and internet sites
Used PowerPrep to go through questions until I found no new questions. I reviewed explanations for the questions I could not get right in the gmat club forum and other internet forum, and re-take the questions until I got them right.
Verbal:Focused on SC by going through each question on OG and PowerPrep mainly.
Learned idioms, and grammar by getting information from OG, internet sites etc.
Also learned vocab using flashcards (almost 1000 words)
Tried to speed up reading by trying the speed-reading method (actually it worked because I could read faster than I used to)
I thought I did study the right way, so I don't know what to do more or differently.
I even feel I am the stupidest person in the world - because I could not improve a single point even after the intensive study...
Suggestions, advice or cheers for me???