The normal course of breastfeeding actually involves nursing a child for several years. This is what our species is designed to expect. Early weaning, by age one or even younger, is the result of western culture's perversion of the breast's purpose and the overwhelming promotion of infant formula. While infant formula offers no benefit to a baby past nine or ten months, human milk continues to benefit the child for as long as he takes it. Receiving comfort and nutrition at mother's breast for several years is something that children in many traditional cultures enjoy.

One cannot possibly know if a child gained what he or she needed from the breastfeeding relationship unless the child is allowed to self-wean. Typically, a child won't self-wean under three years. When a child is said to have self-weaned earlier than this it has usually been the result of a mother unwittingly substituting nursing for comfort with pacifiers, food, or a lovey object, or the child went through a nursing strike due to teething, illness, or some other upset in his or her life, and the parent didn't diligently offer the breast through the strike in order to continue the nursing relationship.

The normal course of breastfeeding appears to be about 3-4 times an hour. In traditional cultures in which children are mothered at the breast there isn't usually a large decrease in nursing frequency until sometime in the third year.

Unless your pregnancy is considered high-risk, there is no reason why you have to wean your baby. As it is, your eldest child is still dependent on human milk for optimal development and will be for some time. Plenty of mothers nurse throughout pregnancy and go on to nurse two children after the birth of their second child. Proper nutrition is key- make sure to take in enough calories for the three of you, and rest is important.

Your milk supply has dropped because it is changing back to colostrum for your newborn. Colostrum is present in small amounts because a newborn's stomach is very small and inelastic. When your mature milk comes in (and it probably will more quickly than with your first) you will have plenty of milk, enough for both children.