Just to clear up the facts before im shot down.
If the jill gives birth to a small number of kits, i.e four or fewer, then she likley to return to oestrus about two to three weeks after the birth of the litter. if the jill does come back into season,she should be mated immediately; if she is not, the raised levels of oestroegen in the jill will inhibet lactation (i.e milk production)this causing potential fatal problems for the kits in the litter and even the mother.