How often should i have to do a pt/inr blood test while taking coumadin (warfarin) long term after massive pulmonary embolism ?

Depends : initially every few days. Eventually hopefully once every two or possibly more weeks. Whatever you do make sure to get tested. If you take Coumadin (warfarin) without monitoring it can be very dangerous.

Warfarin monitoring: How often your INR needs to be checked depends on the stability achieved on your dosing regimen. On the average, if stable INRs are established, checks every two weeks or sometimes less frequently are done. If the INR isn't stable, more frequent checks are often necessary.