Hey Jenny,
The best tests to figure this out are MRIs or Bone Scans. I had a bone scan last summer to rule out rheumatoid arthritis. I had joint pain everywhere. The bone scan came back totally normal. So no inflammation was present at all. Turned out the joint pain was actually my Fibromyalgia. Pain in the muscles/tendons/ligaments that surround the joints. The pain feels like it's right inside but it's not!
I'm just wondering if all your tests come back normal, including a normal sed rate, you might have Fibromyalgia. Do you get aching, burning pain in any of your muscles? Do you get joint pain that moves around quickly and doesn't settle in one place for very long? Your rheumy is the only one that can diagnosis this. I'm just thinking out loud!!
If it's lupus causing this, you'll likely have an elevated sed rate and your knees will be swollen and red. Do they look and feel like that?
I hope this helps. A little brainstorming can go a long way. Let us know how you do okay,
Ginny