Hello Bianca,
Your post interests me a lot. I hope my questions and comments help you work with the staff/professionals in your area.
Your son has received therapy for his speech but not for language? This is concerning, because from what you have described, it sounds like he has classic symptoms of language impairment which is very similar to aphasia. (The condition actually used to be called childhood aphasia because the symptoms resemble those of adult/acquired aphasia.) You have described limited vocabulary, word retrieval difficulty, circumlocution (talking around something or describing it rather than using a specific word), formulation difficulty (putting his ideas together and figuring out how to express his thoughts), grammar errors, and so on.
As to your son's speech production/articulation--are you saying that many or most words start with the n or d sound? Has he had a thorough articulation assessment recently? What is worked on in therapy? Are you given daily home practice to work on with your son? It sounds like his articulation is way behind age expectation, and he should be in a very specific, highly focused therapy program with a plan.
Has your son had any treatment using AAC (Augmentative/Alternative Communication) using electronic devices?
It is no wonder he stays close to you! Consider that you were traveling in a foreign country and you had only rudimentary skills in that foreign language. Would you venture very far away from your travel guide? This is analogous to how your son may be feeling.
Has the neuropsychologist completed a full battery of tests with your son? DId he report to you about your son's cognitive skills/intelligence? If so, were you told your son has at least average intelligence? If yes, then, again, your son's profile of speech-language difficulties sounds like a classic speech-language disorder and he deserves very intensive treatment.
Why do you think the neuropsychologist only commented on your son's fine motor skill issues? Do you think the behavior issues you went to that specialist about resulted from his communication difficulties and frustration? How frustrated is he?
I agree with you that dropping your son into school will likely be very overwhelming for him without a lot of supports in place. In the US students like your son receive testing and an IEP (Individual Education Plan--or sometimes it is called an Individualized Educational Program.) Do you have such a thing in your schools?
In my view, you are not obsessing. You are aware that he has significant needs. You are your son's strongest advocate, and he needs a lot of help at this point in his life.
I hope you will write back.
Best wishes to you and your son.
Mary Lou
Mary Lou B. Johnson, M.S.,CCC-SLP
http://www.helpyourchildspeak.com