I've been having pain behind my knee for quite some time now, it's like a deep dull achy throb. If I sit for a period of time and get up it the first couple of steps end up in me limping. The pain has started to get worse and has become very painful whilst at night in bed where it seems to be waking me throughout the night. When I get out of bed the pain makes me limp. I've contacted the doctors today as it's becoming unbearable (I was hoping it would go away) any way he seemed to have felt a lump and is referring me to have an ultrasound and orthopaedics. 
Has anyone experienced anything similar?