I've been getting headaches for the first time in my life (41). Last one was persistent tension for several days but moved around back and top of head. Clean CT scan w/o contrast, no mass/effects. Normal exam, no vomiting or nausea etc. Tumor Likely?

Can't be exact about. The cause of headaches because there are several major types, e.g., vascular, sinus, muscular, tension, etc.
Please see you doc so he/she can examine you and give you the proper treatment for the type of headache you have. Consider biofeedback and/or clinical hypnosis (www.asch.net) after seeing doc. Peace and good health.