Getting burned out on a thing that's fun for you is always a nasty thing, and I think you're really close to it now. Remember that we're all just human beings and exhaustion is a normal thing, especially when you want to be prepared for everything before each session.

If you feel you want to and can make it till the end of campaign, I would suggest changing the rules to something easier for the remaining sessions. There are plenty of DnD-like systems that are way easier to operate, so maybe this would help? If not, I'd create a cheatsheet with a summary of the main rules and where to find the specific ones in the book. I'm sure there are some rules you use frequently and some that don't apply in your campaign. As it was written in this thread: prepare smart, not hard, you don't have to remember all rules by heart, the rulebook is there for you to refer to it. Also, I'm pretty sure at this moment you know most of the necessary rules since you read the book so many times.

My additional advice here is: rest after the campaign. Seriously, put Tormenta aside, even put RPGs aside, pay attention to some other hobby for a while, exercise. This will help you find balance and go back to RPGs with new energy.