My creation kit randomly crashes throughout using it but when I load my plugin (tomb.esp), skyrim.esm and update.esm up it says "FORMS: Duplicate form ID (02000D62) encountered in file 'tomb.esp'. It removes all the progress that I started before.

I'd look in TES5Edit, find the errant XX000D62 Form, then R-Click > "Change FormID" > XXFFFFFF, updating any reference info if necessary. CK won't handle a duplicate FormID very well, as you've seen, but TES5Edit should let you get in there and fix it.