My cat had her second litter almost 6 weeks ago. 4 very healthy kittens but the one born first, the smallest as well, started to become the quieter one. At first I thought nothing of it but today it was by itself I went over to check and it was very cold. I've been keeping it warm but it won't touch food, water or kitten milk, the other is showing no interest. What can I do it's completely limp, please help