You're a good parent to be worried and quick to look for solutions, but look at it from his perspective for a bit. When he stumbles and your demeanor changes, he will read that as a stress sign because you are his main source of validation. If he senses your worry and is suddenly taken to all these appointments with people he's never met before, that is bound to make him think that there is something wrong with his speech when he hadn't previously recorded any problems. He might be stuttering more now because he focuses on his speech more now. He wants things to return to the way they were before and he doesn't want to disappoint you. The fact he said 'I can't' means he recognizes the underlying tension. It's a good sign he's expressing that though. If he stutters on 'I want to go to the park,' work on your demeanor not changing. Instead, get him to talk more by asking open-ended questions such as 'Why do you want to go to the park?' 'What do you like to do at the park?' and so forth. Fewer yes/no questions. That's a good way for him to develop his thoughts and speech. And in cases like the other night when he said 'I can't,' hug him and ask him 'What is it he can't do?' and how does that make him feel and reassure him with affection.