I had that too... I don't know why... I just thought that maybe I got sweatier after I had kids and was breastfeeding and I noticed that my skin (arm pits) would get more itchy as the hair grew in... versus, before i had kids it was not like that.
Its weird.. I dont' know why...
But also, after I had kids and I got more sweaty and my "B.O." smell got, well, 'stronger' I've had to used stronger deodorant too... so "maybe" my skin reacts to that?
But then, the body just generally changes after pregnancy too... the hormones, and probably even the chemistry make-up of your sweat changes, and everything... so maybe 'sensitivities' to things are more heightened...?
I don't know, but my arm-pits do not itch all the time, nor anymore... and it wasn't constant..but enough that I noticed.
But I would take a Claritin/antihistimine... and it seemed to help. But I can't really pinpoint the "why" my armpits itched thing.
It will be interesting to see what others say...
all the best,