I may be totally misunderstanding the way you're doing this, but I infer
from what you wrote that you're aggregating a bunch of days into a week,
then aggregating those CALCULATED week totals into a month, then aggregating
those CALCULATED month totals into a year, and so on.

If that's the case, it would probably be easier if you had calculations
within each record that simply spat out separate fields for the week, month,
and year numbers, then did the totals on each of those individually.

For instance, today is 2010 May 5. If I create a record with that date
auto-filled, it could have calculated fields for Week = 18, Month = 5,
Quarter = 2, and Year = 2010. Then you could do your sorting and totalling
on ANY of those fields individually. Heck, if you wanted to, you could even
have a Weekday field that would let you isolate all activities on Wednesdays
(or any other day) for subsequent analysis.