For The Past 2 Months, My Husband Is Having Discomfort

For the past 2 months, my husband is having discomfort below the left breast and sometimes goes around his back. He says it feels like the sensation you get from a TENS machine. It comes and goes. Sometimes and mostly at night. He does do a lot of burping especially when he wakes up in the morning. This burping in the morning has caused him to vomit a couple of times. What could this be