What Causes Shortness Of Breath, Abdominal Bloating And Fatigue?

My husband is 74 years old and in the past couple of months he s complaining of shortness of breath, abdominal bloating and just generally not feeling well. He works part-time in a garden center from Spring through Summer and has been off now for several months, so he s had nothing to do - no hobbies, etc. He s been checked over by our family doctor - tests were run - but nothing is showing up yet he still feels in his words, like I m dying.