not getting all notifications

I've noticed I'm not getting all of my notifications. For example someone will send me a text and my phone will not notify me. The only way I know someone text me is if I go into my messages and see it, this doesn't happen all the time just sometimes. Another problem I've noticed is that my phone will not ring everytime someone calls me. I'll get notified of a voicemail and I'll be like why didn't my phone ring? The person on the other end tells me that it rings on their end. Again this doesn't happen everytime just occasionally.
I have an iPhone SE running ios 12.3.1. Any ideas?
Thanks