I posted here elsewhere, maybe you'll see that post, but food allergies is often the culprit. I get hives and skin rashes on my legs when I eat the wrong food. Also more joint pain when I eat dairy or gluten -- I THINK. Haven't really tested that theory enough yet but I think that's what's causing joint pain. Regular blood tests won't tell you anything about this and I don't know why medical docs won't recommend food allergy tests.