Hi, MissChelseaStitt,
Perhaps you could provide more details.
The only way that your iMovie library "updates" is if you import media into the iMovie library. The imported media will display in the Media Browser when you click on the library's name in the media sidebar. By "media library" do you mean the media browser screen for the iMovie library? Are you saying that videos imported into the iMovie library have quit displaying in the media browser screen?
Media that you import from time to time into your Photos app library's system library will display in iMovie when you click on the Photos item in the iMovie sidebar. Are you saying that videos currently placed in your Photos app library have quit displaying? If so, maybe you have "Photos" selected in the selection menu in the upper right of the browser screen, instead of "Videos" or "All".
It might be helpful if you could post a screen shot of what you are seeing.
-- Rich