If your table(s) in your BSVW have a dedicated column for month and year, you can create a level-break footer section on the month column changing (sort by year, month) with both sorts checked for level breaks.
If your table(s) do NOT have month and year as separate fields, you will need to perform the level-breaking logic yourself. This should not be too complicated. Sort by date. Extract the year and month for every record read. If either value changes from the prior values, perform a custom section that outputs the totals for the prior values (manual level-break footer). You will need to tally the totals yourself.