Onset of stammering in adulthood could be a signifier of anxiety or stress, less likely is the possibility of an throat pathology. To find out the cause behind your stammering it will need to be understood that how did the problem begin, in what circumstances did you have stammering in beginning, what are the circumstances where it is exaggerated, other symptoms, your smoking history, etc. The doctor is likely to examine your throat for any other cause. My suggestion to you is to visit a psychiatrist as of now, if so required an ENT consultation can be sought subsequently. Hope this helps you.