This drug is an odd choice to treat lupus... do you have RA and lupus perhaps? Sulfasalazine is most often used to treat Crohn's or Ulcerative Colitis, and also used to treat Rheumatoid arthritis. This drug has a sulfa component that many with lupus would react to (sounds like you don't have this problem at least) and has also been implicated in drug induced lupus.
At one point I was given a drug with a similar sounding name, but it was just an NSAID drug. If you fail to show improvement soon, you may want to ask your doctor about this drug choice again and see if/when you should go off it.