What to do if my girlfriend isn't replying?

Look at how her replies have been shaped over the last few weeks, not just the last one. If she has always been slow, two days of silence is ordinary and you're reacting to nothing. If she used to answer within hours and the change came after a specific moment, like a disagreement, a missed plan, or a rough week at work she mentioned, the silence is more likely to be about that.

Also check what you last sent. A message that asked her something she had to think about, or that needed a decision, often sits unanswered because it feels like a commitment. A light message with nothing to solve is easier to answer. Your last message may have made the silence longer without you meaning it to.

Three kinds of message tend to work here. The first is a low-pressure check-in that references something she told you about her life, like a trip, an exam, or a friend's wedding, and asks about it without assuming she has time for a long answer. The second is a small, specific joke or observation tied to something you both share, which gives her a reason to smile and respond without carrying any weight. The third is a simple, plain question that is easy to answer in one line.

What these share is that they're short, they don't mention the silence, and they make no request for her to explain herself. Avoid anything that reads as a test of whether she still cares, or that stacks two questions so she has to pick which one to answer.

If you've sent one message and heard nothing, give it at least a full day, often longer if she's usually slow. Don't send a follow-up the same evening, and don't check whether she's online every hour. A second message a day or two later is fine if the first was light and easy to ignore. Keep the second one even shorter, and don't reference the first.

If you've sent two messages across roughly a week with no reply, that is an answer. Stop initiating for a while and let her come back. If she does, respond normally without bringing up the gap. If she doesn't, and the silence goes past a couple of weeks, it's reasonable to send one direct, calm message asking whether things are okay between you, then accept whatever comes back.