HI,
Zoloft (sertraline) is used to treat depression, panic disorders and anxiety. Nausea is one the
side effects of the drug. If Ondansetron is not helping there are other drugs like antacids and proton pump inhibitors that can give relief. You can ask your Doctor for a change of prescription. Also dietary modification like eating a bland non-spicy food, avoiding alcohol and smoking will help.
The answer is based on information provided.