I've taken warfarin since 2007 now and had a few knocks and bangs with one thing and another, but never any sign of a bruise or anything
Ellen; I've taken Warfarin even longer and had regular blood tests, often weekly, at a path. lab, and they focus on my INR level. Too high and my thinner blood produces bruises easily; too low and no bruises, so they adjust my daily dose accordingly. Seems like your INR could be low. It's a life choice; too thin and risk a brain bleed; too thick and risk a clot! As someone said, life wasn't meant to be easy! 
Btw; I've found as I've matured that my ego bruises far less! 