Remember that Lupus is an auto-immune disease, characterized by the immune system suddenly deciding that some normal, healthy body part is foreign and needs to be attacked. (In normal people, the immune system only attacks viruses and that sort of thing.)
So it's quite possible that the top of your foot, and/or your ankle, is suddenly red, swollen, inflamed, and/or painful for no other reason than that Lupus has decided it's foreign.
I personally had a long period where the tops of my feet were painful and couldn't stand being touched, but there was nothing wrong other than Lupus inflammation.
Has your Dr given you permission to increase your prednisone (if you are even on it) when you have a flare? If so, you might try that. If not, it's perfectly reasonable to call your rheumy and ask permission to do that, or ask to be seen.
Lynnwood, Lupus & Sjogren's Moderator, Dx: 2002DIAGNOSING LUPUS & HW's LUPUS 101
"Life is far too important to be taken seriously." - Oscar Wilde