Pivot Table with Distinct Values

Hey, Im using Excel 2013 and I know about the Distinct Count but I cant figure out how to turn dates into months if I make the data a table.

I am having trouble creating a pivot table that shows the current total of unique transactions by month. In Column A I have a list of invoice numbers with the invoice numbers repeating if two different items were ordered from that same invoice. In column B I have the date.

Invoice Number
654522
654526
654526
655112
582945
699422

Date
1/7/2010
2/3/2010
2/3/2010
3/1/2010
3/15/2010
3/27/2010

I understand that I can convert my columns into a table and do the distinct count. The only problem is that after I do the distinct count I don't know how to group the months.

In summary, How do I get a distinct count and then group by month?