Has anyone every had dark bloody mucous post nasal surgery?

I had endoscopic nasal surgery 3 weeks ago today. Everything has been fine. Finished a round of antibiotics and have had no problems until today. This morning I woke up a bit congested just on the right side. When I blew my nose a VERY thick, completely dark bloody mucous came out. It has been this way all day. It builds up and then when I blow my nose, it all comes out, lots of it. I plan to call my ENT tomorrow morning, but was just curious if this is normal, even 3 weeks after the surgery. I haven't had any blood come out of my nose since right after the surgery. It concerns me that this happened all of a sudden. Anyone who has had sinus surgery who has any ideas what may be causing this? Any input is most welcome :-)