Why are you not replying to my message

Start by looking at what she sent before your message, and what you asked her in return. If she was replying quickly and warmly and then stopped right after you asked a heavy or open question, the question is the likely problem. Open questions about her favourite place, her job, or her last relationship can feel like a lot to answer by text when she's on her phone at lunch. If the conversation was already slowing down before you sent anything, that tells you more about her interest than the message does.

Also check whether she replied to every single thing you said. People often skip the last line of a message and answer the first. If she answered one part and ignored the rest, she may have replied and you missed it, or she may have only had time for the easy bit. Either way, the thing to do is respond to what she did say, not repeat what she didn't.

When you follow up, the message should be something she can answer in five seconds without thinking. A small observation about something she mentioned, a light question with an obvious answer, or a playful line that invites a one-word reply all work. The point is to lower the effort, not to show that you noticed the silence. The moment a message refers to her not answering, the conversation becomes about her not answering, and that is the last thing either of you wants.

A draft is the right kind if you could send it to anyone and it would still make sense, but it only lands because of something real she told you. It should contain one thing to respond to and nothing to apologise for or explain. Leave out any reference to how long it's been, any question about whether she got your message, and any second question stacked on the first.

If you sent a message and got nothing for a day or two, one follow-up is reasonable. Wait at least a full day after the first silence, and make the follow-up noticeably lighter than the original. If the first message was a question, make the second one a comment or a joke. Send it in the daytime, when people are more likely to be checking their phones casually, not late at night when it reads as chasing.

If that also gets nothing, stop. Do not send a third message, do not like her photos to remind her you exist, and do not send a message saying you're fine if she doesn't reply. Give it a week before you consider reaching out again, and only do that if something new has come up that gives you a reason to write. Otherwise you've got your answer, and you're better off putting your attention into someone who is replying.