I have three baby chics, two are about three weeks, and one is about 4 weeks. One of the younger two, a Buff Orpington, seems to not be growing as well as the others. The other that is the same age, a R.I.R., is about twice the size of the first, and has tons of new feathers. The Buff Orpington seems to be staying away from the others and not eating as much, also always seems to be sleeping. Is this a sign of sickness? If so, what could it possibly be? Is there anything that I can do?