For A Week To 10 Days, My Husband Has Experienced

For a week to 10 days, my husband has experienced queasiness in the stomach, occasional tightness under the breast area in the upper abdominal area. He eats well but feels slightly nauseous all the time. Bowels may be a little darker if anything although he is taking pepto bismo tablets to help. Any idea what this may be? He has always been healthy and had a normal colonoscopy last year. He is 60 years old.
Thank you.