There are so many reasons that can cause chronic fainting. This is certainly something that you should discuss with your doctor.
I know that one reason for fainting can be a nervous system disorder and Lupus can cause disorders in the central nervous system. However, I cannot say if this is the cause of your fainting because, as I mentioned, the list of causes is quite extensive.
Do talk to your doctor about this so that tests can be run to find the exact cause of your chronic fainting.
Peace and Blessings