I would like to create a PivotTable to count the total sales of each
product
for each month. However, I am having problem to do the count by month.
Currently, I have to add another Month column

You don't need the extra column. Assuming you have Products down the side
(Row area), dates across the top (Column area) & Count of Product in the
middle (Data area):

Rightclick a Date cell across the top & choose "Group and Outline -- Group"
from the pop-up menu. If your data spans years, you'll need to group by
month *and* year.

HTH,
Andy