IPhone 4S not alerting me of messages?

My phone will randomly not notify me of a message. The alert doesn't show up on my lock screen nor does it ring/vibrate but then ill unlock my phone & there will be a "1" on my messages app and I'll have a message from forever ago. This is very frustrating because yes I do miss the vibration sometimes but i usually just click the power button to see if I have an alert & it will say I don't, but when I unlock my phone there's a message. Yes, I've checked the side button & yes I've checked my settings for alerts. Does anyone know how to fix this problem? P. S. My software is up to date

Go settings, notificatikns and turn messages on. Mke sure your ringer is all the way up, they won't display in the lock screen. Unless you go into settings, messages and hit allow in lock screen

Sweep up menu from the bottom and turn off the "do not disturb" looks like the moon symbol