You will have to pull it out to have a look.
Replace the flywheel that is suited for they clutch in you have at the moment.
Or, replace it with a Exedy heavy duty clutch and flywheel.
Exedy make clutches for Nismo.
But having said that, when buying an Exedy clutch, that does not make it a Nismo clutch.
Exedy have the license to make the clutch kits for Nismo, but to Nismo Specs.
If you buy an Exedy clutch, you must use Exedy parts. Nismo clutch, use Nismo parts.