What I probably think is wrong with your phone is if you have dropped your phone or if it's getting old then you definitely need a new one also here's some strong advice if your phone is getting old I highly suggest you get it repaird I had that same issue the battery wasn't working right and I had it for a long time also if you dropped your phone you might want to get it repaired.

What you could possibly do is I had that same problem before if you haven't backed up your phone for more that a month that's probably the issue, but also if your phone is getting a virus or something like that you should definitely get it fixed, but if it dosn't work then you definitely need a new phone If you have a android then u probably need a new SIM card.