Make sure you weren't mistakenly logged out somehow and double check your settings make sure no one else has access to your account. Also try logging in from a desk top and see if it's the device or entire account that's buggered up.
Since you're not receiving emails on any device, I recommend checking your Gmail app. Sounds like settings may have been changed or disabled. In the phone you can go into the setting > apps > Gmail on your device and click clear data. This will reset this Gmail app back to factory settings and you can re-logim into your Gmail and set it up as you would've when you just got your device. Hope this helps.
Also if you're using low power mode, that prevents Gmail from delivering email notifications until you manually open up Gmail. If you're struggling with your battery, turn off 120Hz. It's a big help.