Are you doing actual weightlifting (mostly near maximum strength) or bodybuilding? Doing 3x10 sets I can easily exhaust myself to a point where I'm mentally unable to do anything serious afterwards and need days to recover. After weightlifting (powerlifting/olympic), I usually have a lot of mental clarity and recover more quickly. Also: are you taking long enough breaks between sets?
I'm happy to hear you're doing everything right (but the part of me that was hoping for something easy to fix that could help you enjoy lifting more is a bit sad...). Using a watch for timing breaks is something I'll pick up, thanks for mentioning it.
