I get nausea a lot (no pain), but rarely vomiting. I was told that it was one or both of the following:
1. Something is off-balance in my brain and it is interpreting stimuli (smells, eating food, etc.) negatively, hence the strong nausea being present much of the time. In order to treat this, they can do a low-dose SSRI or tricyclic to "reset" the brain a little bit. I did that for a while and don't take it anymore.
2. My current rheumy explained to me that I have extreme intestinal slowing (not gastroparesis because it is not my stomach, but my intestines). When food is supposed to be anywhere from 50-100% through my intestines, mine is only 3% through (eek!). He said that this could contribute to that nauseous feeling just because things are moving SO incredibly slow. He attributes this slow rate to SLE, saying that in my case the SLE is likely affecting my peripheral nervous system, which can affect the nerves in organs like the intestines. He told me that lupus is unlikely to directly attack the GI system (meaning to cause damage to it like it may the kidneys, lungs, heart, etc.)...it isn't impossible, but is very rare. He said it is much more common to have the nerves affected, which indirectly affects the GI tract.
Good luck! I still take Zofran/ondansetron as necessary, but take it much less these days. I've really just tried to cope with the nausea and to eat when I can without overdoing it and causing myself more nausea.