I'm sick of losing my chickens....

I'm not having a very good few months with my chickens.....and the saga continues. I lost another of the sussex girls a few days back, she came down with respiratory distress, actually both of the remaining sussex girls did, but 1 of them was quite a lot worse than the other, and she consequently died, despite my best efforts, with lots of TLC and antibiotics, but the other one has come good. And then, this afternoon, I returned from being out for about an hour or so, to find one of my little plymouth rocks girls dead in the pool.  We have had a pool for probably the last 14 years or so, and I have never lost a chicken to drowning in our pool. Poor little thing...I was here all day too, other than going out for the school drop off and pick up....I don't know if it would have made a difference, but I think I would have heard something, some flapping around or something.....So, I am now back down to 9 chickens, and I think I will just keep it this way for the time being. We aren't getting any eggs at the moment either...just to add insult to injury....the last 12 months or so has been horrendous with losing chooks, the previous 15 years or so was no problems, we have lost more chickens in the last 12 months than probably in our entire 18 1/2 years of being here....other than when we had an issue with a fox, and nearly our entire flock was wiped out in 1 night about 14 years ago....I'm really hoping all of the bad luck with my feathered friends is past us now.....