Is It Safe To To Sex After 21 Days Of Microgynon?

Hi, i have recently started taking microgynon to deal with severe PMS and heavy, irregular periods. I am on the ones you take for 21 days then have 7 days off. I have read in a few places about running 3 packets together and only having the 7 days off once every 3 months - I would like to do this but wanted to ask if it is safe to do so?