Our internet works but my ipod says unable to join network. It was working a little bit ago

It could be a couple of things. It might be an issue with your WiFi router. Have you tried resetting the router? Then try reconnecting. Another issue is it could be software based. You could try first backing up your device on iTunes, and then try resetting the iPod to factory defaults by wiping it. Has the iPod been dropped or gotten wet? Check liquid indicators in the earphone jack and inside charging port. There should be a tiny white strip. If the iPod has had any water damage this strip will turn pink or red. Water damage can cause many of the functions to not work properly. Hope this was helpful