My 4 month old had 3rd lot of jabs yesterday. I also changed his formula from sma to amptamil as read on here it was better. Today he has had a couple of incidences of watery poo. He has no temperature and seemed a little better after the poos but still a little bad tempered.
hm - tough call. I changed from sma to aptamil at 2 weeks and B didn't get watery poo, but it did get a lot runnier - had been quite firm, formed stools on sma, now her poo is the consistency of - eh - single cream, I guess. Nice!
But B does get the squits after jabs, so going by my experience it's that. Which isn't to say it's the same for your bubba.
Either way, as donnie says, it should settle soon.