All Categories change to Uncategorized

Every couple of weeks when I log onto my WordPress account all of my Categories change to “Uncategorized.”The only solution I have found is to call my host and have them reset my site for a few days earlier. However, this happened to me over the holiday weekend and I am afraid that it may have been happening for longer than 7 days (the allotted back up time)so I need a more permanent fix. Does anyone know how I can restore my categories to my hundreds of posts? PLEASE HELP!