Heavy Bleeding 4 weeks after surgery

I am 58 y/o and in good shape and had nerve sparing robotic surgical removal Nov 16 at Mayo. Until today, everything seem to be going normally, just the usual leakage of clear urine and occasional pains but nothing requiring meds. I’ve been off work and taking it pretty easy. However, this morning when I first voided I was alarmed to pee very dark brown like coffee. No pain just thick dark brown and small clots. Since my surgery my flow has never been more than 50% of normal. I called and spoke with a nurse and she seemed to think this likely will clear up in 24-48 hours and to drink plenty of fluids which I am. But I still have colored urine although not nearly as bad. Has anybody else had this or know what could be the cause?