Queries :: How To Sort Records By Grand Total Descending

I've recently been building a database on Access to replace the rather clunky and slow one we currently use here (built in Excel).Generally, I've been making it up as I go along which has worked quite well for me so far. However, I've encountered pivot tables. Normally, it shouldn't be a problem; the tables themselves are easy enough to understand. However, I've found that the tables aren't nearly as flexible as I would have liked. At least, not in a way directly apparent to myself.

(After trying, and failing, to include links to Imgur with details on my issue, I have included a .zip file with both images I was going to show)Generally, in Excel, the table works everything out for us, then we sort by largest to smallest and work out the totals for the last 7 days and the last 7-14 days (the week before last). After that, the last formula works out a percentage (loss or gain). [excel.png]

In the access table, though, I can't find a way to make this happen. There's no readily apparent button to add a new calculation field. I've tried using the create calculated total button, but that seems intent on making a separate total for each day on the table, which I don't want. [access.png]

Also, I can't figure out how to sort the records by grand total descending. I would have thought right clicking the grand total and clicking sort descending would have done it, but apparently that would be far too easy. I feel that it's prudent to mention that I'm not all that experienced with Access. I completed MOS and ECDL courses when I was in primary school, but it's been a really long time since that and all of the Office applications have changed rather dramatically.