Why does my cell phone keep getting an error message about my password being wrong or account being changed?

I do not have Google+, I do not have 2 step verification, and I have no data to show in my data tools tab online. So, why do I keep getting an error message that my password is incorrect or my account has changed? I didn't change anything, in fact, I never use it. Have I been hacked? If so, how can I resolve this so it doesn't keep happening?