sciatica pain is a nerve that provides for the legs/buttocks. It isn't a nerve that would do anything about the stomach. However some peeps pain can give people upsest stomachs and nauseous just by itself.
I do have sciatica issues but never had any vomiting feelings, just a lot of leg pain.
I don't, however, mean to leave you with the idea---on any level---that you should be thinking about spinal tumors