3 years ago I developed a bad strep throat infection

Patient: 3 years ago I developed a bad strep throat infection and mouth ulcers, a week later I woke up and could barely move my legs, ever since my knees often become slightly inflamed and very painful and I end up with bruises the days after and my knees are permanently purple and very cold, I’ve been tested for arthritis and it came back negative, I’ve been suffering for 3 years now and when I’m very tired my elbows become very painful too, any ideas on what it is that is causing this?

Doctor: