My daughter is 25 weeks old and formula fed. I would say she has spent more of her life constipated than not. Generally though, despite settling into a less than ideal pattern of going once every six days, when she finally did go, there would be a LOT.
We've started weaning a week and a half ago, and I so hoped that having something other than formula in her system would make a difference, but in fact it's worse than ever. Today she strained like mad for a tiny, hard poo 
I've been making a point of giving her a good 6-7 oz of very diluted orange juice (I struggle to get her to drink water) to the detriment of her milk feeds, as there just aren't enough hours in the day to get five milk feeds, two small purée feeds and one bottle of "juice". This past week she's been having four milk feeds instead of five.
But I digress, despite a little sugar water yesterday, having a prune based purée for dinner AND breakfast AND a little diluted prune juice, she's as constipated as hell.
I'm really worried because I suffered horribly with constipation all through my childhood and beyond, and read plenty of horror stories on here about children with faecal impaction and all sorts of nasty bowel problems. It seems worryingly common and I don't want her to suffer like I did.
I have some Lactulose upstairs (leftover from the postnatal period, ahem) so would it be worth starting her on the baby dose of 2.5ml 2x a day? I REALLY want to nip this in the bud, so any advice re. progressing with weaning would be great.
I prepared an ice cube tray with prune purée for future breakfasts (book). Luckily she seems happy to eat pretty much anything, so guess I'll start with that!