What Causes Vomiting, Nausea And Belching?

I am 75 years old. About 3 years ago I started having infrequent bouts of nausea. These are always before or after the noon meal. I can feel my stomach tighten up and feels like I have eaten rocks. The nausea starts with some belching or swallowing to force the movement downward. I never have heartburn. Then I start to involuntary spasms of the stomach like I will vomit. Most of the time I will completely empty my stomach in one or two or more sessions of throwing up. I can go for months without one of these events. Sometimes there will be four of five a month. Any ideas or questions?