I fell down some stairs last week, which didn t hurt too badly at the time, other then bruises, and continued with my daily routine which includes working on a farm, riding horses and prolonged sitting in class or driving. I have had fairly bad back pain the past few days ( and my pain threshold is quite high) concentrated in my tailbone which makes it difficult to lay down as well as walk around, (standing is fine). I found a small hard lump at the bottom of my tailbone with bruising on either side of it. It hurts more when you press on it and continues to ache more after pressing it then before. Around the same time that my back pain started I have also found knee pain in my right leg that also hampered my daily activities, and ached all day. I m wondering if the two things are related, and whether I need to see my doctor this week.