What's going on with these toilet habits? 9 weeks

[TearingMyHairOut]

My ds1 91/2 weeks goes to the toilet every 2-3 days. When he goes it's expolsive and huge and quite runny and yellowy mustard colour (bottle fed). He's obviously not constipater because it would be more solid right? The thing is, the day his poo comes he is really grouchy for several hours before hand, like a severe blockage and then as soon as he's been he's ok again. What's going on here?

Same thing happens with ours, every third day he can not seem to go and is bothered by it all day, then will explode the following morning - using SMA gold & considered changing because he seems to be in pain yet when he does poo, it is soft and mustard coloured.
We give Tom hot baths on bad days & cooled boiled water inbetween feeds to try & help him.

we've tried three different formulas and not seen any difference

TearingMyHairOut - Really? Maybe babies act like this then until their tummies mature a bit more. Our HV suggestged dilluted prune juice - one part to ten parts cooled boiled water - we did try it a couple of times but it made his poo very loose, so I don't think he was constipated and we have stopped reaching for the juice each day now because we don't want him to get a lazy bowel.
I read somewhere that babies have no control over the muscles down there for quite sometime and can not consciously choose when to go - so if they have tummy ache, even if they are not quite ready to go, they will try - hence being grouchy and preoccupied - don't know if this is true but would make a lot of sense.
Its difficult though isn't it, because you can't distract them. Hot baths do seem effective and if our baby seems to have quite bad tummy ache, we give him some Calpol, which relaxes him after about half an hour.

I would say if he os not in any pain and it is still runny it should be fine. Just the way he is.
DS is breastfed and goes rarely but I do know on the day when it going to happen because he is grouchy etc.
DD who was formula fed by 5 months was the same and she never went every day until she well established on 3 meals a day.