You sound like you've had a real frustrating run with GRE prep so far. It's hard to tell from your description whether you feel you have a solid background in the content knowledge. Find out how are your pre-algebra, algebra, geometry and data/statistics skills by analyzing your errors. If you discover, for example, that you keep getting exponents or geometry questions wrong - you might want to try a skills workbook like an ACT Math prep book. (I use Richard Corn's ACT book). Don't be afraid of trying innovative techniques like plugging in unusual numbers for the variable-based quantitative comparisons.