5 years old with a poop size of a coke bottle !

[3under5babies]

Hello
my sons when he poop everyday his poo is soft and normal size. But every two weeks his gut just stop working and he doesn’t poop for three days straight resulting In massive poop size. But other days when he goes everyday, the poop are skinny type 4 sausages. Skipping poop for three days happen only maybe every 2-3 weeks. He drinks plenty of water 1.2-2l and eat plenty of fruit and fibre. Diet is not an issue because he goes for a poo everyday and it is soft, it’s just when he get that episode. How can I stop his poop going big when he skips pooing for 3 days !
it’s hard giving him movicol or laxative because it makes him go 2-3 times a day.
should I just ignore these episode , can it cause any damage to him when his poop goes big if he skips a poop?

If there's no other worrying features (eg blood, straining, not wanting to go) then it's ok to have the occasional big poo. You could keep a bit of a food diary to see if anything obviously to blame for the spells when the gut is slower?

If you have laxatives, you could try a smaller dose (eg using half a sachet instead of a whole one).