Correct Display Settings Only Apply after restarting X

[echoz28]

Whenever I start my computer, GRUB will show up on the middle monitor and the right-hand one, then I've set mint to start in text mode (TTY1), and it also runs on the same two monitors. Now if I type startx, only one monitor will be used and my icons will be mashed together on one side of the screen. Restarting X will make it run on all three monitors exactly as intended, but I don't want to do this every single time I start my computer. Does anybody know how to fix this and make it run correctly at the first login?

Side notes:
When I go back to TTY after "fixing" the issue, it shows up only on the middle and left-hand monitor.
I also added a script that sets my primary monitor to the middle one to startup applications.
I'm running Linux Mint 14 MATE 64-bit. My system specs are: AMD Phenom II X4 @3.4 GHz, 8 GB DDR3 RAM, AMD HD7850 2 GB GPU.
Also dual-booting with Windows 7, through GRUB 2 bootloader.
(I'm new to this forum so I'm very sorry if I did something wrong, e.g. posted in wrong section or whatever.)

Thanks in advance