You can say, honey, what's wrong with you? What's so boring? Is there a problem? Tell me ... and make her happy. You can take her to eat something delicious, go out for fun and go shopping. In this way, girls' mood will be broadened and they will not feel bored. The most important thing is that the boyfriend must take the initiative to take care of her in time.
If a girl has no strength to talk, you should care about it and ask her how she is. Maybe this girl has her period, but not necessarily.