The only reason I've seen for a database to get very large is when there is a picture (JPG file) used in a form. Apparently Access does not do a very good job with storing this type of data. Perhaps your database has an image stored as a data item in a table (or some other place.) Other than that...no idea why you should see such a large size.
Alternately, you can create a new empty database and then copy each object from your current database to the new one, one at a time, and check the size of the new database after each copy. That will at least identify which object is causing the problem.