This is my first attempt at chickens. I got 15 layers who are doing fabulously, and 25 cornish x. One of the meaties died right away, but I've lost 4 more since then--2 today! They are almost 3 weeks old. I have them outside in a tractor with a heat lamp and a run. I move it daily. They have continual fresh water, and I started feeding them 12 on/12 off at 2 weeks. They're on medicated started crumbles. The poop doesn't look bloody even a little bit. What do I need to do???