You can do the calculation at DB level if you are using tables as source but otherwise check the links below.
it should help.
Neither link you provided helps. In my original text I said I know how to get YoY (quick calculation) but don't know how to get the difference between the current month vs three months prior.
Current month you can get using now() function in tableau.
Three months prior you need to extract the month part from now() and subtract three from it to get three months prior.
hope it answers your question.
Not sure what are you looking for.
Current Month: MONTH(NOW())
Three months prior: MONTH(DATEADD('month',3,NOW()))