Invoice problem with extra details on line items

I have been asked to create invoices on my database, there are 3 tables to
reference, the orders_header table with the order number and customer
details, the orders_detail table with the line items, descriptions,
quantities etc, and the orders_comments table, which is linked to line items
on the orders_detail table.

The problem I am having is getting the orders_comments data up onto the
report.

I have a report with a subform. This subform holds the line item details.
Linked to this I need to have the table with the orders_comments data, but
each invoice may have 20 items, of which only one line has extra comments,
but these comments in turn, may reside in 3 or more fields.

What is the best way to approach this problem? I have tried unsuccessfully,
as the result I keep getting is the comments repeated under every line item,
not just the one they are meant to refer to.