How can I tell whether my husband has a terrible illness (which he is keeping secret)?

My husband is not well, and will not tel me what is wrong. Two weeks ago, on Thursday, I came home from women's fellowship, and my husband's doctor was at our house. When I came in through the front door, he came down stairs from our bedroom putting his shirt on. He seemed distracted, and shortly after, his doctor came downstairs. My husband explained that he was worried but was sure it was nothing, and his doctor didn't add anything (she was observing his privacy, which I respect) but I could tell she was concerned and worried. Last week, my husband had to return to the doctor for a followup appointment, and was gone for 3 hours. When he came home, he seemed exhausted. I am worried that he has leukemia or something horrible like that. How do I get him to tell me what is wrong? This weekend, he is going in for overnight observations and testing, and will not be back until Sunday afternoon (he will be missing church). I am worried. What should I do?