I stutter on a word at the start of my sentences, but I can speak perfectly fine when I say that word in the middle of my sentences. Does anyone know why this happens?

I stutter on a word at the start of my sentences, but I can speak perfectly fine when I say that word in the middle of my sentences. Does anyone know why this happens? For example, I cannot say the word 'apple' as the first word of my sentence. However when I say 'the apple is good', I do not stutter at all. This is very frustrating for me as I have been forced to add extra unnecessary words when I have been speaking to my friends.