Dr. Wants me to do CT scan of abdomen bc of stom. Cramps, not able to lose weight for 6+ mos. Skeptical bc I had CT of chest negative/ all tests neg. Feeling extreme nauseated today. Help? Radiation?

Have the CT scan. The ct scan is one of the best ways to determine the cause of abdominal pain. Radiation exposure is modest and not a clinical issue.
You are right. About the radiation exposure unless the benefit outweighs the risk. Would hate to second guess your doctor with no specific information. Ask your doctor what he/she is hoping to confirm or rule out by the scan.
Abdominal Pain eval. A ct of the abdomen is part of the evaluation of abdominal pain. However it certainly is not at th ebeginning of the evaluation. A through history and physical exam. Then consideration for less expensive blood work including liver and pancease blood tests and possibly stool studies. In a 21 y/o female the commonest cause of abdominal pain is constipation, followed by acid related irritation.