Pivot table displays month and year; but not month in both columns for 2017 and 2018

Thanks, Jan.  I believe I answered my question by doing the report with anonymised data.

When I added the activity period field to the field list, it automatically checks quarters and years.  I unchecked quarters and then had 2 columns on the pivot table for 2017 and 2018. 

Then I clicked the + sign by both 2017 and 2018 and presto!  My months are sorted in calendar order!

Thanks for your assistance!