My knee is really hurting, only it isn't always in the same place so sometimes it's under the knee cap and then other times it's at the back of my knee, sometimes the pain goes down my shin sometimes into my calf and sometimes in the side of my thigh. It wakes me at around 4am despite me taking painkillers at 11pm. I'm not stiff when I wake and can walk without pain. Then when I sit down in the evening the pain starts again. Any ideas please?