mscporter
Hi there - I spotted a couple of things;
1. Usually around 6months LO drop their catnaps, is your LO actually tired or are you giving a catnap because it is what you have alwyas done? Try and reducing the length of the catnap
2.Try and aim for a 2hr 'A' time from wake up - or at least build up to this.
3. He is possibly on the verge of getting too much day time sleep.
4. What does he do in his 'A' times, is your LO being stimulated enough, the reason I ask is you say he is awake from 4/4.15pm from catnap then is yawning again at 5.30pm and ready for bed again.
Considering he goes to bed at 6pm, at wakeup of 5.30-6am is excellent. If you start extending 'A' times you will naturally increase his day and start to push the bedtime out to a later time in increments.
HTH's
Lauren