Add weight method, 8,8,6,6,6 Basic muscle groups. 2-3X a week. Automatically takes into account bad or fatigued days because you don't go as high in weight.
Every couple months I take a week off to get the enthusiasm back.
Changing up routines has never done anything for me. Did all the periodization schemes, "muscle confusion" crap, etc. This is the best approach I have found that works long term.