My Husband Has Experienced Abdominal Pain, Diarrhea, Nausea, Vomiting For

My husband has experienced abdominal pain, diarrhea, nausea, vomiting for over 3 weeks now. He has lost 16 pounds over this time and is not able to eat much prior to feeling full. He is also tired all the time. The pain became more severe and we went to local er yesterday. The GI doctor on call wanted him to be seen in her office and to try and collect a stool sample. She felt he would need a scope of some sorts. Today, his vomitus changed to coffee grounds look. We went to GI doctor in the practice of the one was consulted with yeterday. He did no exam on my husband and told us he had two theories - viral gastroenteritis or diabetic gastroparesis. He said that if he continues with pain and other symptoms over the next two weeks call back for further testing. He was not concerned about the coffee ground vomiting , but did say that if he continued with the vomiting, to go to ER to check for diabetic ketoacidosis. I did not feel confident in this diagnosis and treatment. Do we need a second opinion?