A small child crying usually can't tell you what's wrong. They can only tell you that it's wrong, loudly, in the middle of a supermarket. You don't argue with them about whether they're overreacting. You pick them up and start working out what happened.
Pain communicates about that well. Back pain that's really eight months of clenching. Fatigue that's really grief. The signal is honest and the diagnosis is useless.
Meeting it with irritation, not now, not this again, teaches nothing and helps less. What tends to work is the tone you'd use with the child: something in here is uncomfortable, it isn't lying to me, and I'm going to find out what it needs.