Not an uncommon problem Karthikeyan. About 5% of children are still not dry by night at this age. However, you do need to see a pediatrician about this. After a through history and examination your doctor will be able to reassure you completely and provide strategies for coping with it.
Please look up this excellent resource. I used to refer parents to this when I was working in the UK. Most of this is relevant to us here in India too.
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