Many women do get pregnant while breastfeeding, so weaning isn't necessary. But you're right that breastfeeding can make it a bit tougher to conceive. It's actually designed that way by nature to provide optimal spacing of children. Women in some cultures don't have effective forms of contraception, and breastfeeding serves as a child-spacing method. In these populations, where moms breastfeed into the second year of baby's life and beyond, babies are born an average of every two to three years. (Still, you shouldn't use breastfeeding as a form of birth control — it certainly isn't foolproof. Some exclusively breastfeeding moms regain fertility soon after giving birth.)
If you still aren't having regular periods (the prime sign that you're ovulating), they should return as baby gradually eats more solids and takes less milk from your breasts. And even if you continue to breastfeed frequently, your fertility will return eventually.
In one small survey, women breastfeeding longer than one year and not taking hormonal birth control resumed menstruating at an average of 14 months. (The first few cycles are sometimes anovulatory, but they usually signal that your fertility is on its way back.)