Hello from JustAnswer. This is Dr. Love and I will be assisting you today.
I am sorry that your husband is having so many problems.
It certainly is true that any metastatic cancer can cause systemic symptoms. Since the cancer is growing greater than other tissue, it does leach much of the caloric intake, so fatigue and weight loss are common. Shortness of breath can also occur, although it is less common in someone that does not have disease int he lungs or significant anemia.
Of course, it is appropriate to consider whether other conditions are present, but if there are no other condition identified at his regular check-ups, it is appropriate to say that the symptoms are due to the cancer. Obviously, I cannot examine him over the internet, so I cannot say with certainty that I agree that the symptoms are due to the cancer. But I can say over the internet that it is common to have such symptoms, and is particularly likely in someone without any evidence of other conditions.
Yes, the enlarged lymph node is considered a tumor. The term, tumor, simply is a generic term that refers to any solid growth, so includes many condition other than cancer, but also can refer to any solid growth of cancer, either in the original organ or if it starts to grow in a lymph node or any distant organ.
If I can provide any additional information, please let me know.