Still sneezy..

I posted a little while ago when two of my buns were sneezing, one with nasal discharge too.
The vet reckoned it was just an allergy to a new hay I used, and I did think it was rather dusty at the time but I let it air and the buns loved it which is why I kept giving it to them. Obviously after the sneezes I chucked it all out just incase.
However, that was about the 8th of April, and both buns are still a little sneezy. I took them back to the vet yesterday and the vet listened to their chest and had a checkover and doesn't think it's anything more serious and was reluctant to give antibiotics because of the chance of it making them more resistant to it in the future.
However, I just cleaned out their litter tray and popped in their normal hay, Rex jumped straight in like he does, then sneezed about 20 times in a row :?
Is it possible the allergic reaction to one hay has made him more sensitive to others, or would he still be 'recovering' from the 8th?
If he is allergic to all hays now, what do I do instead? Buns are indoors and used to a lot of veg but as two of them (not Rex) have molar problems I don't want to remove hay from their diet, but I wouldn't want to split them either as they're a tightly bonded trio.

Have you tried only providing hay in hay racks, maybe it's the jumping in and disturbing it all that is getting it up his nose? Might be worth a try for a while to see if it makes any difference :?

do you use pine woodshavings? That could be the cause....

I don't use woodshavings for any of my animals anymore. The rabbits are bedded on newspaper (had Vetbed but as one of them wees everywhere it needed washing far too often and it only just fits in our washing machine and doesn't wash as well as it should) with either woodbased cat litter or Megazorb in the litter trays. I put the hay in their big litter tray as they're all toothless and when Mary used to have a hayrack he didn't seem to be able to manage to pull much out without his teeth. Rex has never had any sneezy problems before the other week, and as you might've seen from the 'spot the bunny' pic I posted the other day, he does love to sit amongst the hay!