2. The bristles of your toothbrush look worn out.
Many people brush their teeth the wrong way. It’s because they either brush too hard or use hard-bristled toothbrushes and this damages their teeth. So if your toothbrush is looking like it needs to be replaced every couple of weeks, then you’re brushing too hard (and need to try and fix your technique somewhat). You should replace it after 3-4 months, but even then it should look pretty healthy.