How old are you? I’m almost 45 and in the last 5 years or so I’ve noticed my body will revolt against certain exercises. For me it’s usually a matter of doing too much without adequate build up.

OP I get those same pains. If they weren’t clearly hormonal, I’d join the PT chorus, but they’re obviously hormonal and it’s not from muscles loosening. Use heat, massage and choose different exercises when the pains prevent you from doing your regular workout.