Hi there, have you figured it out yet?!
If it hurts during/after eating, particularly if you eat something sour (bite a lemon and see how it feels..), it might still be a salivary stone. Eating, particularly sour/bitter things, stimulates saliva flow and if there is a stone blocking the flow, this causes an increase in swelling/pain.
I'd suffered with swelling and pain and numerous infections for at least a year. After a really bad infection that caused so much swelling I couldn't move my jaw without immense pain, the infection never seemed to really fully go away, and for months my gland was so consistently swollen my friends would "joke" that I had a tumor.
This was when my doctor FINALLY decided to recommend me to an ENT and I recently had quite a large stone surgically removed from my submandibular gland/duct. Solved ALL of those problems.
My doctor had first ordered a sialogram but then when I went in to have it done, the DR at the imaging center said he believed an MRI would be a better option... so I had an MRI done both without and with the reactive dye.
It is important that you review these images yourself, as well as letting your doctor look at them. Particularly if they claim that there is no stone (in my case, I could FEEL it, so I knew it was there... so I found it preposterous when the report came back saying there was "no significant swelling of the gland" and "no calcification present". )
They gave me the CD to take to my ENT, and before going in I looked at the images on my computer. There were hundreds of pictures, and my mother and I sat down and looked through EVERY. LAST. ONE. (it helps if you are familiar with anatomy) And saved the ones that very clearly showed the stone to my computer and wrote down the picture numbers.
Had I not done this, my ENT may have looked at the report and not looked at the images himself and said that it wasn't a salivary stone.. or he may have missed it too, because it was only clearly present in maybe 4 pictures out of ~450... which is weird because it was pretty large (my ENT said it was one of the largest he'd dealt with). He immediately referred me to surgery, and less than a month later I was healed and better. So when I went in, I just told him which images on the MRI CD to look at.... LOL
ANYWAYS, my point being... perhaps you should have an MRI done in addition to the sialogram. Lupus *may* be the cause of it, but salivary stones are also common with Sjrogren's.
Hope you get it figured out soon!