You can run it for any day of the week and go back to the week previous to that. Try the below code see if it helps you:
=if(DayName(CurrentDate())="Sunday") then Sum([Measue Object) Where ([Date Proposal Sent] Between (RelativeDate(CurrentDate();-8);RelativeDate(CurrentDate();-2)))
Elseif(DayName(CurrentDate())="Monday") then Sum([Measue Object) Where ([Date Proposal Sent] Between (RelativeDate(CurrentDate();-9);RelativeDate(CurrentDate();-3)))
elseif(DayName(CurrentDate())="Tuesday") then Sum([Measue Object) Where ([Date Proposal Sent] Between (RelativeDate(CurrentDate();-10);RelativeDate(CurrentDate();-4)))
elseif(DayName(CurrentDate())="Wednesday") then Sum([Measue Object) Where ([Date Proposal Sent] Between (RelativeDate(CurrentDate();-11);RelativeDate(CurrentDate();-5)))
elseif(DayName(CurrentDate())="Thursday") then Sum([Measue Object) Where ([Date Proposal Sent] Between (RelativeDate(CurrentDate();-12);RelativeDate(CurrentDate();-6)))
elseif(DayName(CurrentDate())="Friday") then Sum([Measue Object) Where ([Date Proposal Sent] Between (RelativeDate(CurrentDate();-13);RelativeDate(CurrentDate();-7)))
elseif(DayName(CurrentDate())="Saturday") then Sum([Measue Object) Where ([Date Proposal Sent] Between (RelativeDate(CurrentDate();-14);RelativeDate(CurrentDate();-8)))