Apple ID login keeps popping up after turning on iphone?

Recently whenever I turn my phone off or when my phone dies, I power my iphone back on after charging or turning it off and I keep getting a pop up that asks me to sign into my apple ID. I never had this problem until it started yesterday. I tried rebooting my phone and turning it off and on but the pop up kept asking me to enter my apple ID password. I went into settings and I was signed into Itunes, Facetime and icloud but I wasn't signed into imessage. I noticed every time I turned on my phone I kept getting signed out of imessage so when the pop up came up and I entered my apple ID password I realized it was signing me into imessage and I noticed while I did this it said "waiting for activation" under imessage in the settings, and after a minute or two it then activated and worked normally. How do I stop my phone from logging me out of imessage everytime I turn my phone off because the pop up is extremely annoying and I'm tired of entering my apple ID password over and over, any tips would be greatly appreciated, thanks.

You need a new phone