Aura-
Hi.
You can tell your hosts that “For medical reasons I cannot eat any bread, especially white flour bread” – I’m sure they’ll have no problem with that.
There are breads made with non-wheat grains that people with allergies and intolerances use.
If those aren’t an option either, you may want to ask a Rabbi what alternatives exist for hamotzi in your case.
Health is important – there’s no obligation to eat foods that make you sick.
Good luck.