IMessage Issues

Alright, first of all, I have an iOS 11.2.6 iPhone 7. I am new to the community and have only had this phone for about half a year and I know very little about the systems, having come from Android. I have had the same problem repeatedly, and suddenly, for months now involving my iMessage suddenly stopping. I go to text and suddenly it shows that it is waiting for activation or I have to put in my Apple ID. It is very irritating and I don’t understand why it stops working after looking up possible solutions dozens of times. I have turned my phone on and off and that helps get it back on track, but it is only temporary before it stops working again. I have changed my password a few times now, hoping that would work but to no avail. I’m confused and need help to finding a more permanent solution otherwise I feel like I will have to return back to Andriod. Thank you for your time.