Hi Leigh,
It's quite common to experience weight loss. I had chronic anemia about 2 years before my diagnosis. I lost a lot of weight. I looked anorexic actually, but ate like a pig. The lupus was attacking my blood, causing the anemia. As soon as I got diagnosed and started treatment, I gained the weight back. In spades unfortunately.....
What are you taking for medication right now besides the plaquenil? If you're losing weight and on prednisone, that would be something to bring up with your rheumy. That shouldn't be happening. I have no experience with plaqenil and its side effects. But someone here will know for sure if that's what it is.
I do know that plaq takes many months to kick in, so that might be why you're still losing weight too?