Lupus can cause gastrointestinal disorders. In fact, many with Lupus also have Crohn's disease, gastritis, and celiac disease as an overlapping illness. All of these diseases can cause vomiting. Many of us also have IBS, but that occurs mostly in those of us who have Lupus and Fibromyalgia. I would suggest that you contact your physician and make him aware of this as soon as you can.
If your vomiting is accompanied by headaches and muscle spasms, please please see your doctor immediately as this may be a sign of serious Central Nervous System involvement or other serious conditions.
I hope that I've been helpful. Please let me know if you need something further.
Peace and Blessings
Look For The Good and Praise It!