you have your period, and feeling a little crampy, and because of that you were kind of stressed, you were just lying in bed under the sheets and you didn't want to talk to anyone, not even Childe, and he noticed that you she wasn't well, so she went to try to comfort you

"what are you feeling dear? Are you in pain? Or are you stressed? Do you want me to make a warm water bag to see if the cramps go away a little?"