I know what you mean about
being one's own physician...
Significant weight loss can be caused by thyroid issues e.g. Grave's Disease... this can happen to people with Lupus, maybe that is worth checking on if it hasn't been yet?
Regarding GI issues I will just throw out there: eosinophilic colitis; intestinal endometriosis; or an intestinal pathogen such as actinomycosis, brucellosis, intestinal tuberculosis, disseminated histoplasmosis etc. Some bacterial pathogens in particular will seek out the ileocecal junction and if you are immunosuppressed as treatment for lupus this could be a possibility.
Also will just throw out there I have Crohn's at the terminal ileum but the worst LRQ pain I personally experienced was from a large ovarian cyst...went on for two months till it finally ruptured... Now THAT hurt. If you've already had an abdominal/pelvic CT or ultrasound that would have ruled out this possibility.