Hello Erika and welcome
When a doctor suddenly says, you might have "that" and leaves you to ponder that information, it can be, understandably, very worrying.
As the others have said, there is a lot of old and even incorrect information on the internet concerning lupus. For some people it can be more severe but for a vast majority the newer treatment methods will mean that life can go back to pretty much normal.
Maybe putting your mind to preparing your trip to the immunologist will help you relax a little. I don't think that it is good to OVER-read and inform yourself but, for example, taking a look around the information "stickies" at the top of the forums on this site, reading the info on the main site here,
www.thelupussite.com and some other reputable hospital sites such as the St Thomas's trust, the Mayo clinic and so on might help inform you a little.
Try to clearly note down your list of syptoms (even those you think may not be related) and also keep a diary of what's going on with you. All these things help us be clearer when we see a doctor and give us something to refer to if we suddenly suffer from white coat syndorme in front of the doc.
AND bear in mind that lupus is a highly complex disease. Diagnosing it isn't easy and it can also "mimic" many others.
I hope that appointment goes well and if in the meantime you have any questions please don't hesitate
Katharine