gmail search – all my emails over 30 days old disappeared in all my labels and unable to retrieve them

All the emails over 30 days old in my Gmail account(all labels including in box, sent, all mails and trash) had disappeared. All these emails were deleted without my knowledge. I set up different labels to store all my important emails over the years. Have not checked them for a while and was very shocked to see them all gone when I tried to look up a 2 months old email that I stored in one of the labels. I’ve tried many different ways to retrieve it without success. I also changed the passwords and different settings with no luck. Does anyone have the same problem? Wonder if my Gmail account has been hacked? Any advices on how to successfully retrieve old emails in Gmail account?