Ich gone; now fungus?

It seems (in my admittedly limited experience) that every time we
treat ich in the aquarium, we then get fungal infections. There are
no signs of ich now (treated with King British - seemed to work
faster than Protozin) but a couple of the fish now have white
patches, including what looks like a ring of white fungus around one
or both eyes.

I'm treating with Melafix, which dealt with this last time - but is
it common to find that after treating ich, other diseases occur?

(This is the first time we've used King British - before we used
Protozin, which should have taken care of the fungus too, shouldn't
it? - it didn't though.)

--
FishNoob