Could my 18 months of fatigue,weightloss and gastro issues be related to an occult hormone secreting small cell lung cancer. nothing showing on ct.

Unlikely to be small: 18 months of active ongoing symptoms and still. Itching on CT ... Unlikely to be small cell lung cancer , which is relatively an aggressive form of lung cancer. I'd suggest you get reassessed for other causes of weight loss/ fatigue - especially concentrating on gastrointestinal causes , thyroid disease or even diabetes. See your doctor again.