Issues with SumX Function -- Table Totals Incorrect

Hi Greg,
Here is my current formula. I tested you suggested DAX query, but I had an error at the end referring to '__Result'

For clarification, I am recycling Weekly NetChange from another formula I have written

Here is what the measure looks like: WeeklyNetChange =sum('Weekly Sales'[Weekly Sales')

Here is a sample of my data. I have used a star schema linking my vendor ID to my calendar table. I recieve weekly reports I am looking to subtrack the current week sales to the previous week sales based on report date.
Additionally on the table I do not get the correct generated total for the Diff Current Year Weeks and Previous Year Week. 

When formulating a similar table for MoM and YoY, the chart is able to filter and tally the correct totals. 

Let me know if you would like more information.

Thank you for your time and clarification.

Kindly!