Access & PostgreSQL Question

Where I work we have a database to track what our employees do each day. The database was originally created in MS Access but grew too large and unwieldy for Access, so we migrated it to a PostgreSQL database server and continued using Access as a front-end, due to its ease of use and familiarity for management.

Recently I was asked to add a field to the table that tracks the individual tasks and now Access is reporting this new field as the primary key, which has resulted in any lookups to change entries that contain errors pulling up the same record from five years ago, and taking several minutes to do that even. I have tried removing and relinking the table, as well as creating a totally new database and linking the table there, with the result always being the incorrect field linked as the primary key.

My question is: is there a way to force Access to either use the correct field as the primary key or force it to ask which field to use as the primary key? Alternately, is there another application other than Access that would be as easy to use that would communicate better with PostgreSQL, as well as be available for free (corporate doesn't like to give us any money for software, or we'd be running MS SQL Server)?