I was having back pain while sitting on my couch and also i was about to get a cramp in my leg.  When i got up i all of a sudden got chills and was really cold.  Around my knee it feels like a sting and is red all over and when i touch it it feels very hot.
The symptoms you are describing points to different pathologies. Your low back pain with some stiffness can be attributed to lumbar spondylitis with some neuropathic pain called as lumbago.  However, the swelling, pain, redness around your knee joint suggest some inflammatory either infective or non-infective pathology. Please mention duration of symptoms and associated systemic symptoms.  I will suggest consulting a rheumatologist. Hope my answer will help you. Take care. Don't forget to rate me.