Like all things, and when there is pain, have it checked out by your doctor. It may or may not be related to the medicine. Vomiting acids damage your esphogus lining. Are you drinking enough with your medicines? sitting up, and not laying down? Time of day may effect it too like at night time before going to bed instead of in the morning. Taking meds with food or not? Constipation can cause nausea, vomiting too. I sleep on an incline bed, which helps with acid reflux. Other medications, vitamins can cause acid reflux or GERD, food too or lack of. Even chemo can damage the mucosal lining from your mouth down to your tail. Some use Glutamine powder mixed with water to help repair tissue in the mucosal lining, helps with neuropathy too, aloe Vera juice also, which is slightly laxative, but that may help with pains meds causing constipation.

Good luck, and hope you find some answers, relief.