Can I use a liner when I have my period?

Yes you can

Yes, you can use a liner when you have your period, but only if your flow is really, really light. It’s best to use a U by Kotex® Ultrathin pad (they’re really thin), or a tampon as they provide the best protection while you have your period. Liners can be used as a back up in your undies if you’re using a tampon. Everyday Freshness Liners are best for keeping you fresh, confident and protected in-between periods.