|Let's say your dates are in A1:A5.|
In 2 cells someplace else (you can hide the columns later) enter these formulas.
For the purpose of this example, I'm going to assume you used B1 and C1.
B1: =WEEKNUM(A1) and drag it down to B5
C1: =MONTH(A1) and drag it down to C5
To count dates from last week and last month, use these: