I just got a RAT9 as my first gaming mouse and have found the transition very easy,
If you are struggling after five months I'd try and identify the underlying cause,
go back to a normal keyboard and familiarise yourself with the mouse first, get used to pressing a certain button instead of a key on the board or moving the mouse and clicking,
most mice have profiles for browsers as well as games so set your browser profile up and maybe put your keyboard hand behind your back
MAKE yourself use the buttons you have assigned to functions and it won't take long before your brains trained to use that method instead, freeing up your keyboard hand for other things or just making its life easier by having less to do,
I trained my brain for WASD/mouse gaming using Portal and Portal2, very forgiving sandbox games, then moved onto Alice2:Madness returns which has smarter enemies and requires a little faster responses,
Mass effect series and now I'm on Crysis series,
Once you are really comfortable with using the mouse swap over, use a normal mouse and start using the keyboards macro/hotbuttons, same again get used to everything you need/want to,
then when you are happy with that, go full gamer spec on both and your brain should handle it well, if not welcome the new gear because its now used to it,
Some folks take time to adapt, others pick up straight away but keep at it and you should get there relatively painfree
Sidenote, I got my mouse on friday and am now completely comfortable with it, my Kb hand only needs to do wasd and relax
it is often a difficult transition. i stopped using a pc for about 5 years and played exclusivley on consoles in the ps2 era. i tried to use a ps2 type pad when i returned but it was just to slow against keyboard and mice users.
eventually i got used to it again but it was about 6 months of at least 1 hour a day playing games. i did find that the best thing to do is reconfigure the keys for every game the same. so if you use fp shooters make sure you use a consistent layout.
such as switching your G key (often grenade) to E or Q if you use wasd and there not already configured to the typical E= use item or lean.
also if you have a multi button mouse put things like crouch on button 4 and knife on scroll wheel up after a while using they will become second nature as muscle memory takes over...
but like i say its a long learning process and you will have to just use trial and error to see what works for you.
My best recommendation is to make sure that the keybindings that you are using are actually A. functional and B. comfortable. A lot of games come with awful default keybindings, and often times using keybindings that you didn't think of yourself will be harder to remember and ingrain in your muscle memory than keybindings that you lay out for yourself, and that make sense to you personally.
I guess it just takes time to get used to. I've played console games in the past; basically Halo since a friend of my usually likes to have people over and Halo was a fun multiplayer game back then on the Xbox. Anyway, I always it found it to be a bit awkward and not as accurate as using a keyboard / mouse combo.
Just keep playing eventually you will get used to it. And as stated above changing the key binds could help a little bit. Additionally, having a gaming mouse with multiple button can help as well. I play with a standard run of the mill keyboard and a Logitech G500 gaming mouse. The only thing special about the G500 is at you can change the DPI for the mouse movements. I use a low DPI when I am scoped in for a sniper shot and high DPI for doing everything else.
Most of the time it takes time, but a some point the keyboard or mice might be simply wrongly designed for your hands.
Size does matter here, so bigger hands need bigger M/K, etc.
From my side, i am using same mice since a very long time (Logitch G3). As soon as i really started to like it, i went to a store and got 5 of them (currently using last one).
I only know that its a good idea to go to a store and try the keyboards if possible for at least 20 seconds to get the general feel of it. If at start is looks ok'ish, then its probably going to be grreat later on when you get used to it.
If not ok'ish, it probably wont be good later on.
Personally, i am targeting a Corsair K90 and a Elecom-Gm20 now, but the mice turns out to be extreamly hard to find in poland at this point.