I am not able to help you, unfortunately... But I was wondering: do you run a rescue? I see you have so many piggies, you often have babies... now again this sow is pregnant... I imagine you are offering your home to piggies in difficulties, otherwise I don't understand...
And if you have so many pets at home and you run a sort of a rescue, I guess you have also a team of vets ready to ask about these health troubles.
Anyway, you have a great experience with piggies and pregnancies, therefore if you see that this time things look different, you should call your vet. The risk is loosing the mum and the babies and this would be a great pity, although you have lots of piggies around... Pregnancy is a delicate period and yes, the heat is terrible when you are pregnant.