Hi!
My 3.5yo started preschool a few weeks ago and has been really tired since then too..we've moved BT about 30mins earlier and even then DS has also started napping again some days.
He also plays up at bedtime sometimes, lots of callbacks & excuses not to sleep. We try to be firm but fair & consistent e.g he only ever has 3 stories, no more, he can get up once to go to the toilet again but only once & we tell him to get it all out! After that, if he keeps calling us or getting up we just go in/put him back to bed, say goodnight gently but firmly but no other interaction and go out again. Sometimes it takes a bit of persistence but DS always goes to sleep eventually.
So routine, consistency & clear boundaries that we stick to..that seems to work for us
Xxx