How to get last 3 months sales

Hi,

Lets say i have a query like

select sales from test where MONTH(GETDATE())>3 it gives me the past 3 months sales as we are in 6th month, but i want to have something in the where clause which can return me past 3 months sales irrespective of the month we are in, for say if we are in first month of 2014 then i must get 2013 11th month, 2013 12th month, 2014 1st month.

Can someone please help me how to change my where clause to work with this condition.

Thanks