What type of stutter do you have? Do you block on words e.g. no sound comes out, or do you bounce on words e.g. you repeat the first letter of a word? Mmmmmmmmummy or m-m-m-mummy? The exact cause of stuttering is unknown. Mine personally I believe is neurological I have always stuttered since I could first speak. I likely have a genetic abnormality in the language processing area of my brain, as others in my family also stutter. Late onset stammering, like yours may have been triggered by some traumatic experience or something? Luckily for you if you have had fluency before, speech therapy might work for you. Personally for me it's useless.