Amprolium should take care of it, look to see if there are different doses for preventative versus treating an outbreak, may need to mix it stronger. Were they out on the ground a month ago when they got the medication the first time? If not it won't do any good, they have to have exposure at the same time so they can build immunity.
As far as right now, make sure they are actually drinking well on their own, a lot of times they don't feel great and won't drink enough. It might be a good idea to give it to them directly with an eye dropper or small, needless syringe several times a day if you can, until things start to clear up.