Right after a woman gives birth to a child, our hormones are all over the place. If you breastfeed, it gets even worse. When a mother breastfeeds the hormone oxytocin is released into your system. This hormone is what is responsible for "letting the milk come down". This sudden rush of hormones will wear you out. Not all hormones will give a woman this positive effect, many women have had the feeling of weakness, sweating or even an odd sense of trouble. These feelings are normally temporary, but if they become to bothersome then consult your doctor for advice.