Notes missing in my iPhone's Note App

I was using the notes app to put down Christmas presents ideas when my phone exited me out of the app, and when I reopened the app ALL MY NOTES WERE GONE. Google told me to update my phone since I haven’t in awhile but only my shared notes came back. I HAD OVER 350 notes most of which are very important! Please help me. I need those notes

[Re-Titled by Moderator]