Breastfeeding in many women is a natural form of birth control. It's why people in indigenous populations usually have their babies four years apart. This is nature's way of ensuring each child has a chance at its infancy and childhood before the next sibling comes along. It also allows the mother's body to adequately nourish the baby and regroup before she becomes pregnant again.
The primal period is two years, and these years are important to the baby developmentally. During the second year of life, the baby becomes independent of the mother, and by the age of three, the child has developed autonomy and reached an age of equilibrium. A three-year difference in ages is good for the benefit of the children.
At five years, when the older child has developed beyond the four-year-old stage (the second age of disequilibrium, which are 2, 4, 6, and 8), introducing a second child into the family is even easier. The older child has a real sense of self, and easily welcomes a sibling.
Sibling rivalries seem to be much less when children have their own time to develop and mature. Relax, Mama, give baby her time and the next addition will be all the easier.