Many reasons, but when I was pregnant I was incredibly tired, all the time. I slept maybe 9 hours, and would be exhausted within 2-3 hours of waking up. Womens breasts also get phenomenally tender and sore. Not to mention all the hormones that get the body ready and able to start producing a new life kinda sap the sex drive. Those same hormones can make a woman not like her normal self at all, with mood swings in full swing. These factors alone would make anybody less than ready to make love. Give it time, and she will be back to her normal self, and remember, she is going to be very uncomfortable in her own skin for quite a while, so try to be patient and loving.
