Thrush in flock?

My chickens have something unfortunate going on, not sure what, but maybe it's thrush? We have had three die over the past month. They first become hunchbacked and swollen, they are like chicken bowling balls. Their combs droop, eyes are watery, white poop gets stuck to the back end, and within a day or two they are dead. The rest of the flock looks healthy, but seem to be eating more and are a bit more aggressive. They just experienced a massive decrease in laying, at the start of the spring season which was very alarming and unusual. They went from 40 eggs per day to 5 or six for a few days there. Now the laying is back up. I am at a loss. We have them in a mobile coop with electric fence around it. move them to new pasture every week. clean out water containers and coop regularly...ugh.