It's definitely worth figuring out!
It's hard when you're unsure of what the issue may be, but try not to focus too much on either option.
Lupus doesn't always show up in blood work. To complicate things there is no yes/no test for lupus. Doctors have to piece together evidence from blood work along with the symptoms you present with and a full medical history. There are some good sticky posts in some of the forums (sorry, not a technowhizz, have no idea how to link to them, perhaps someone could help?) that explain more about how lupus is diagnosed.
There's also info about how it is treated - it varies from person to person, there is no standard form of treatment reaallly. Some people respond well to NSAIDs, some need corticorsteroids, others go one to need stronger immuno suppressive stuff.
Have a look around too, there are lots of posts that explain how to try to prevent symptoms flaring if it is lupus (staying out of the sun, not over doing it etc.)
But definitely get it checked out - we are not doctors, we can only advise.
Best of luck