Doctors would not normally consider 99 a fever as it seems they don't take into account what our individual "normals" are. But given the chills and the fact that your child was sick recently, I'm going to guess you've caught that bug from him

If you have any other symptoms that aren't typical of your lupus, then that makes some little bug/virus more likely yet.
For me, my lupus fever is close to 100, up from a normal for me of 97-98. I've had my lupus fever most of the last few months so I feel your pain. My "sickness" fever tends to be a little higher - closer to 101. That's how I tell mine apart - the actual temp and any other symptoms I have as well as whether a close contact has been ill recently.
I'm much like some others here have reported where some kind of viral or bacterial infection can really kick off some lupus activity too.