62-yr woman w: diarrhea sudden weigh loss depression insomnia 15 lung nodules appear benign rash on legs. Cbc thyroid pancreas appear normal. Cause?

See your doctor. You should discuss the need for further tests with your doctor including a biopsy of the lung nodules if recommended. You may need a stool sample to test for blood and a ct scan of your abdomen, chest and head.
Carcinoid. Don't be too comfortable with answers here. You need a good work up. Metastases can go to lung from the colon which can give manifestations you have. In addition carcinoids can give same symptoms either from lung or the gut. Small nodules can also be from infections including fungal. A proper doctor-patient conversation and work up recommended.