speech delay after long term glue ear

My 5yr old son has a history of ear infections and glue ear between the age of 18 and 30 months when he had grommets inserted. These have now fallen out and his hearing has been normal for 3 years. He has since had several toncillitis infections and chicken pox but has been very healthy for the past 18 months with only a couple of minor colds. He also had a skin condition affecting his shoulders and abdomen which disppeared about 9 months ago. His speech development has been very slow, starting then stopping. He has no other developmental delays other than those related to hearing loss. He sat at 6 months, crawled at 10 months, walked at 13 months, was beginning to put 2 words together at 18 months when this period of infection began. He has had all immunisations and didn't seem to have any adverse reactions. He became increasingly anxious following intervention for his speech to the point of completely shutting down at these appointments. We stopped going but there has been little improvement. He was born 2 weeks early, natural delivery, no drugs weight 7lb 6oz, breastfed with great ease, gained 10 oz a week! He has had several courses of antibiotics and a general anaesthetic. As I said he has no recurring health or any behavioural issues now at all but the speech delay is still persisting. I have ordered Nat Mur 6 but having read other posts do you think he may need Sulphur first, given the amount of prescription medicines/vaccines he has had? Or do you think his present good health is an indication that his body has already eliminated the toxins from medication and vaccines? Is the Nat Mur 6 too weak? Thankyou in advance.