What Causes Unexplained Bruise On The Leg Causing Discomfort?

i had a sleepless night my left lower part of my leg was really hurting and so i elevate the leg and it felt comfortable for a short time then was hurting again like from my knee down to the muscle and then this morning i got up to look for bengay to massagThe the leg and notice a bruise on the side of my leg. My leg still kind of hurt but not too much but the bruise is still there