DS has always slept well - he has gone down for naps awake since he was very little and for the last few months, we have been able to put him down awake at bedtime and he has gone to sleep without any fuss (before that, he was falling asleep on our bed with me next to him then I moved him into his cot). He has generally slept through more often than not since a very early age - but these last 3 weeks, things have gone pear-shaped and he screams whenever we put him in his cot for naps and bedtime - I have no idea why.
Is this a normal phase at this age and what should I do?