help plz

Your model description is one of a simplistic system. The pen in question is not symmetrical in surface area or mass dispersion. When thrown in the air it is not rotating along its mass centers, nor are the frictional effects of air interaction symmetrical. Your pen is both rotating along its longitudinal center and its lateral centers. Initially the spins have axix induced by the external forces of the throw, not the centers of mass. The mass imbalances are causing direction changes interacting with gyroscopic forces of the spinning pen. If the pen had sufficient time to fall without additional forces of friction it would stabilize into a mass balanced centered single axis spin, although it would not be the pen's visual center by any means. As far as calculations go, you must analyze the system into smaller more simplistic ones then integrate the small systems into an overall complex system.