Source columns not showing in Pivot fields

Hello everyone,
I have recently added in a few columns to my source data table and am trying to make a new pivot table which includes these columns in the Values field. For some reason my new columns aren't showing up in the PivotTable Fields list even if I search for them. I have checked that the named source data table has updated to include these columns, which it has. I have also tried saving, closing and reopening my document to see if this updates it, however that didn't work.
Has anyone come across this issue before? Any ideas on how to solve it?
Thanks