((((((Natalie))))))), I'm sorry you have to go through this. I don't think there is a person here who doesn't understand what you are feeling. It gets really frustrating. Just about the time you think you got it figured out everything changes. As for the ANA, I am not sure why it changes but yes somtimes people have poss. and some time some people have neg. Mine has always been possitive but I know people here who have lupus that have never had a possitive ANA. Just try not to read to much into one test. I have never been diagnoised and my ANA is always around 1:2560! You'd think that high somthing would jump out but nope no answers yet. The best thing you can do is keep track of everything that changes in your body. Aches pain fever joint swelling, hair falling out. rash. mouth sores. The best you can hope for is to be treated for the symptoms even if you never have a yes or no answer. If your doctor doesn't treat your symptoms then you need a new doctor. If your doctor wants to blow things off because you get a neg. ANA you may want to see somone else. Don't give up or feel like a nut case. We all have gone thru that one too. Oh no you do not have to be in a flare to have a possitive ANA. Mine never really changes by much weather I am sick or not. If anything your SED rate would change.
Hang in there sweetie. You are no more of a head case then I am. 
(i'm a bad example)
hugs
carol