I'm sorry for your losses. We've been having a bit of bad luck too. We had 3 BO hens for 3 years without a single issue before we had to move. Now that we're back and back into chickens, we've lost several to various reasons (A failure to thrive, hawk, dog, a couple right after/during hatch...) and it's been difficult to explain to our young sons. Don't give up and don't feel guilty. Chickens can hide their illnesses well and by the time they show any symptoms, they seem to go pretty fast. I've gotten a lot of help on here; keep asking questions. I had asked about a chicken who seemed unwell, and it was recommended I treat for coccidiosis, she got better quickly, so I assume that was it, but I know that even common conditions like coccidiosis can move quickly if you're not sure what you're looking for like me. I also was sure my chickens had gapeworm, but thanks to the folks on BYC, I learned that chickens can YAWN... Lol Like I said, try not to get discouraged. Wishing you the best.