But I never see the discharge, but I smell blood, could it be drying in my underwear?

Look, it's super common to notice a different smell down there, like a metallic smell, which we associate with blood. This can happen even when you don't see the discharge. Sometimes, the discharge is very little and clear to begin with, and it can indeed dry in your underwear without you realizing it was there, but the smell still lingers a bit. If the smell isn't too strong or bad, like a fishy smell, and you don't have any itching or burning, everything is probably normal!