i had a similar thing happen to me the other day in my mouth.
V had mentioned something about Iodine pulling(like oil pulling) so i tried it. the area on the inside of my mouth next to some old dental work(caps, one of them gold) welted up pretty bad. the rest of my mouth was not affected that way.
my guess is that it was stored toxins from the dental materials at that site. it is now an axiom we take for granted that the stronger the reaction to iodine, the greater the need for it. in this case, i suspect toxins stored in tissue. these could be elemental, chemical or biologic. kill a bunch of critters and their rotting bodies and be nasty.
you need to get iodinated. then a weak Iodine douche should have no adverse effect at all. if i were female, however, i would take Iodine internally and use home made CS as a douche.