There's no rhyme or reason to it but talking with your primary care physician is the first step. People stutter as a result from medication side effects, head trauma, etc... There is still a lot of research going on right now but I would start by seeing my doctor and then a speech therapist. My stutter is a neurogenic stutter caused by a traumatic event. Everybody's stutter is unique to themselves, go have it checked out. Best case scenario, stop drinking caffeinated coffee......