I have a knee injury, done it over 18 months ago, no bone damage but there was fluid build up. I was told no MRI as I wasn't in enough pain. Fair enough, I've lived with it now for over a year as it is, not great - can't really kneel too long without it hurting and I cancelled my gym membership as it exacerbated the pain - but liveable day to day.
I slipped over in Tesco the other week. Didn't think nothing of it until a few days later. Couldn't drive, had trouble walking down stairs. Doctor said it wasn't related to my initial knee injury 
and to rest up for a few days.
Herein is my problem - it itches like crazy INSIDE the knee. Like, scratch worthy itching that I can't scratch. It keeps me awake at night. It drives me mental. What is it?! Most importantly, what can I do to stop it??! 
Please and thank you for any suggestions.