A couple of more questions that might help:
1. What Mac OD were you previously using?
2. Did you upgrade "in place", that is, basically let Mojave over write what was on your system before.
3. This is critical: have you been making backups to an external device? If (hopefully) you have been, what software are you using for that?
The first update for Mojave, OS 10.14.1, is currently in the 5th phase of beta testing, and thus should be released shortly. Not sure if your issue is addressed in that update, but thought I'd let you know.