Didnt u read on the box of all logitech mice there is a warning that says "Do not use if u are under 18 years old". So,very simple,wait till u get older and your hand grows abit :rabbit:

i think you should just try to play with two fingers because exactly using three fingers will get your middle finger tired for the reason you stated. plus try to use the side button as well at least the big one because it is configured as MOUSE4 , i use two fingers and just lift my pointer finger from the left mouse key when i wanna change weapons but IMHO you should never use the scroll for changing weapons. Just bing the weapons you need on the keys around WASD and on your mouse so that you just have to click and not scroll. Think of it this way, what if you want to go from rockets to machine gun fast? you'll have to scroll and watch your screen losing attention in the game