1. Girls really started the do not disturb mode: Girls may need to turn off their cell phones on some occasions or hope not to be disturbed.

2. Girls don't want to chat with you: Although this situation is hard to accept, it is possible that girls don't want to chat with you or are not so interested in you.

3. Girls are busy with other things: Girls may be busy with other things, or chatting with others, and have no time to reply to your message for the time being.