today, when urinating, a few times i have some blood during the stream and a few drops of blood afterwards. just now, a black piece of tissue, about half the size of an eraser on a pencil appeared. i am 81, 6'. 178 with congestive heart disease and take Coumadin due to a massive heart attack 11.15.2013. my INR level is at 2.1. what could be causing this health issue? thanks!