I know this may sound daft, but try putting him to bed earlier???
Isla sleeps better at night if shes not overtired, if i put her to bed between 7-7.30pm shes really restless, and often cries out. If we put her to bed between 6-6.45pm then she tends to be great (and actually sleeps longer in the morning too!!)
I a big believer in 'sleep induces sleep'
I might be talking rubbish, but give it a try, it cant hurt!