my shoulders have been properly cooked lately

Been noticing my shoulder endurance is just gone halfway through a session. Like I'll be on something sustained, crimpy, feeling decent, and then suddenly my arms are just... toast. Not pumped exactly, more like dead weight. It's annoying because my fingers are fine and my head's in it. Talked to someone at the wall about it and they reckoned it might just be accumulated fatigue — I've been projecting the same overhang stuff for like three weeks without a proper rest block. Which, fair enough, I probably don't rest enough in general. I'm not sure if it's a volume thing or if I need to actually work on shoulder specific stuff between sessions. I do basically zero rotator cuff maintenance and I know that's bad lol. Might look into adding something short after sessions rather than just collapsing on the mat. Anyone who's dealt with this kind of shoulder fatigue specifically from climbing — was it just rest or did you actually have to change something?