I'm not improving...*sigh*

Okay, so I took the GMAT in July and got a 620 (42Q 3something V). At this time, I was getting around a 640-680 on GMATPrep tests.

I've been doing practice problems, brushing up on basic skills, keeping track of missed problems, learning concepts, etc. etc, but my score simply is not improving and I don't know why.

I took a GMAT Prep exam today and got a 660 (46Q 35V) I feel like my Quant level is decreasing because I started with a Quant 47 and haven't reached it since my second practice test in GMATPrep again.

Breakdown of what I missed:

14 Quant (7 PS, 7 DS) - Looking at the problems, I KNOW I can solve them. I feel like I'm stressing out, and with the time constraint making careless mistakes.
11 Verbal (1 CR, 5 SC, 5 RC)

Also when doing practice problems in sets of 20 (randomly picked - not in order) (using OG12) I miss 3-4 at the most. I feel like my score is not reflective of this.

When doing MGMAT untimed, I tend to get around 680-700. I haven't gotten below a 680 for the last 5 practice tests I've taken. Isn't MGMAT supposed to be harder?

I need to get at least a 700 by the end of October and I don't know what to do. I've been through the MGMAT SC twice and the Powerscore CR twice. I've done countless math problems and gone over my mistakes. I'm just about ready to give up. I don't know what else to do/try.

Can anyone help? Motivation, Tips, and Advice greatly needed and will be appreciated!