Possibly, but it may just be the fact that you have a new baby in your life!
Some women who breastfeed report having a decreased libido, while others report that they actually want to have more sex since they don’t have to worry about pregnancy (if they are appropriately using lactational amenorrhea) and feel more in-shape and empowered with their bodies.
It’s hard to say if a lower sex drive is truly related to breastfeeding or to the fact that having a newborn and the subsequent sleep deprivation leaves little time (or desire) for intimacy! Some studies have showed that formula-feeding moms tend to have sex sooner, while others have shown the exact opposite. Therefore, how breastfeeding really plays into all of this is not totally clear. Some nursing moms will not want their breasts touched during sex or may be embarrassed if they leak milk (the same hormone responsible for milk let-down—oxytocin—also plays a role in orgasm). The bottom line is that open lines of communication are important, and weaning should not be suggested as a cure-all to a subpar post-baby sex life.