But he is playing and responding all right and the rest of the litter is fine what could it be, we are 1st time kittens mother

When is this happening... after a hard play period, or while he is sleeping, for example?

It seems after he is playing or walking about he is getting plenty of the mothers milk and resting as the same as the others doing the same as the others, he seems he doesn't do it when he is a sleep

Thank you for the additional info, because sleeping animals have what appear to be dreams, just as we humans do, and sometimes will breathe harder, just in response to the dreams they may be having.

But, by your description, your kitten appears to breathe harder than it's litter mates when doing the same thing as it's litter mates. If so, this suggests he may not be able to catch his breath as easily or as fast as his litter mates. Situations like that often involve the heart or lungs some way. Since he is just a baby, it may be some sort of developmental problem, such as a heart murmur, or even a mild case of pneumonia, not related to any other conditions. Pneumonia in a nursing animal can happen if it simply chokes while swallowing, and inhale some milk into the lungs.

However, the only way of really knowing what may be going on with him, if anything, is to have him actually examined by a veterinarian, and I would suggest this if it continues to seem that he is not improving, or especially if he begins to worsen.