Continued frustration with relationships and queries

So I thought I figured out how to create relationships and run queries but
now I am running into a new problem. I will do my best to describe it.

I have a table that I am using from prior months with all the Regions,
Sub-regions, cities, and zipcodes. It has multiple months of data. After I
create a relationship between two tables at the zipcode level I then create a
query to fill in the Region, sub region etc, I end up getting 1000's of
duplicates. The table that I am mapping from has many months of data while
the table i'm mapping to has 1 month. How do i tell access to only map the
information once instead of brining over ever instance of a match?