Hi Sharon,I don't see much about adults retching in my search for information, but I knew a mom with a post-Nissen baby (premie with lots of problems) who retched a lot.
Often children get retching after Nissen fundoplication surgery as a result of irritation of the vagus nerve. Here's a study that refers to a medication that they have found helpful:
http://www.ncbi.nlm.nih.gov/pubmed/16291162
I wonder if alimemazine would help you. It would be worth asking!
Wish I knew more to tell you. Good luck finding answers!
Hang in there,
Denise