Yes, unfortunately after pregnancy your sex drive will go down for while. This lasts between one and three months normally, though it can last for up to a year in rare cases.
There are several factors behind this loss of desire: the increase in prolactin, the breastfeeding hormone that lowers libido; the baby blues; tiredness after giving the pregnancy, the birth and sleepness nights with the new baby; the baby’s constant need for attention, the stress of your new responsibility and trying to adjust to family life; difficulty in accepting your post-pregnancy body (swollen stomach, shrunken breasts, extra weight), etc etc.
It’s really important that your partner understands his duty: to seduce you all over again and help you re-discover your sex drive.