Having a few issues all of a sudden settling B for nap time. Previously if he's been UT he'd just play in his cot and eventually go to sleep, or fall asleep easily if OT. However he's now very resistant to lying down, and when I eventually get him to do so and leave he cries immediately

I've tried some WIWO but it really winds him up more, always has. If I stand next to his cot he drifts off in minutes, keeps opening eyes and looking to check I'm there but still goes off quickly

It feels like SA and I'm wondering if it's developmental - he's been potty training the last week or two and birthday not too far off. He seems kind of 'older' in his behaviour and language all of a sudden and quite often says 'no sleep' or 'no nap' when I suggest it. He also had a very rough week sleep-wise last week, I think some was teeth/virus but some of his wakings seemed a lot like DDs night terrors.
Routine just to check though:
WU 6/6.30, not out of bed before 6.30
Nap 11.45/12 at nursery - up by 2 usually
or Nap 12.15/30 at home - pushed this a touch as hasn't seemed tired earlier - up by 2.30
BT 7pm and asleep quite quickly - not having the same issues here
Any thoughts? I don't mind standing next to him for a couple of minutes if needs be but not keen to make a habit of it!