Need to add a calculated field on Pivot Table

I have a table with 2017 quantity and cost $, and 2018 quantity and cost $ - but when I try to add 2 calculated fields to compare quantity and $ value year to year I can't get it to do it I think because my two years, quantities and Cost $ are in the same column in the data sheet so i can't pick 2018 Qty - 2017 Qty as my only column is Qty, cost $, and Year.
What's the workaround to get those calculations?

I've attached a sample file with the two calculated columns I need on the right - but I have way too many rows to do them all manually one by one as you can't copy and fill that down either.

Thanks,
Joann

maybe without PivotTable but with PowerQuery (Get&Transform)