Feargal, our little foster kitten, has been yowling since 7am this morning (it was so bad I had to shut her in the kitchen and then shut the bedroom door so I could have another couple of hours sleep

)
Its hard to tell if she is in pain, as we can't really pick her up yet, but she has also spent lots of the day rolling around showing her belly and has been purring when I've stroked her.
She has just been for a poop (admittedly slightly looser than usual) so isn't consitpated and is eating, drinking and playing / following the other cats around.
Might she be in season ? She's not been done yet - that's going to be a fun day at the vets
She is around 20 weeks old we think - I have no idea when female cats come into season, could this be about right ? How long will it last and should I be doing anything ?
Our boys are all neutered, although the youngest one does like to grab her by the neck sometimes, which I presume is a mating move (quick squirt of water sorts him out

) and she is not allowed out.