CPU and GPU were already fully updated, but I went to download the latest AMD driver (don't know why I didn't already have it) and it worked! Thank you so much, I appreciate it (you actually helped a few of my friends having the same problem too).
For anyone coming in the future I figured out the solution.
you wan to use
KeyMapping.click(Minecraft.getInstance().options.keyAttack.getKey());
to simulate initial click and if you want to hold down left click afterward just do
KeyMapping.click(Minecraft.getInstance().options.keyAttack.getKey());
Minecraft.getInstance().options.keyAttack.setDown(true);
and you can switch KeyAttack for other keys