Why do I only stutter with specific words?

Why do I only stutter with specific words? It started when I was around 15, and its mostly with with the words “what” or “did”, when I ask questions only. Its so irritating and embarrassing because it takes me like 5 whole second to get it out and by the time I ask the question the person just stares at me blank faced cause of the amount of times I stuttered :’)