Well, first you need testing, then turn around and educate yourself. Read, read, read. Everyone has a different way about this, but according to the state of Maine, MG is in the wild bird population and if you test negative, then you need to hold onto your birds, keep them from mice, rats, wild birds etc. It is spread trans-ovarian and perhaps we should ALL have our birds tested, especially anyone that does sell eggs or birds. This could be nothing, or something, stop and begin one step at a time, and get tested.
According to the Diagnostic lab here in Maine, there are no hatcheries testing for anyone of these conditions, only NPIP (pullorum and typhoid). So if you have a clean flock, a sparrow roosts on your fence, poops, you bird is exploring what just dropped, now you have these conditions.
The showing industry across the country- they have chickens with "colds" all the time and also find show birds die, oh well.
So after you decide what YOU want to do, breathe, it takes more then 2 days to diagnose in a lab, then go from there. You should contact those who ordered or bought hatching eggs, let them be aware and that you will contact them as soon as you know more.
So many have foofoo'd my beginning worries, and it seems as though others are now believing that these conditions that many have neglected for so long, its showing.
I certainly hope that you find only the simplest of issues, its not easy, very frustrating.
Take one day at a time, cross the next bridge when you come to it.