Report Writer - 'This Week' Reports

Question

Hello there, 
 
I was wondering if anyone could tell me how to generate a report using Report Writer that works on a time frame that effectively is 'This Week' or 'Last Week' in a similar way that there are 'This Month' and 'Last Month' reports. 
 
I would like to be able to generate an uptime report for certain equipment for a given week number which I can then schedule to run using Report Scheduler to email the report off to a third party. 
 
At the moment I have a 'Last 7 Days' report which is summarized by week which is fine except that no matter when I seem to schedule it to run I always get 2 week numbers appearing in the Week column which makes the report less meaningful. 
 
An example of this is shown below: 
 
Somebody Network Ltd - DSLAM
 This report shows the average DSLAM availability over the last 7 days.

Node ____ Average Availability ____ Week
 DSLAM1________ 99.87 % ____________ 15
 DSLAM1________ 100.00 % ___________ 16
 DSLAM2________ 99.93 % ____________ 15
 DSLAM2________ 100.00 % ___________ 16
 DSLAM3________ 99.79 % ____________ 15
 DSLAM3________ 100.00 % ___________ 16 
 
Ideally I would like to be able to just schedule a report to run for 'Last Week' or 'This Week' that would give me the stats for a single specific week i.e. Week 15 or Week 16 
 
Thanks in advance for any help and suggestions. 
 
Andy