Hello erinlealewis,
Thank you for reaching out in Apple Support Communities. We recommend to review the settings on your iPhone to ensure that the notifications for the Messenger app is turned on. There's a variety of different options to enable the notifications for the Messenger app which you can turn on. You'll want to go in Settings > scroll down and locate "Messenger" > Notifications. From here, please make sure that "Allow Notifications" is turned on and then you can configure to select how you would like to receive your notifications within that section, along with the option to select "Messenger Notification Settings."
Following these steps may help.
Kind regards.