Its not uncommon for that to happen, and the fact that you already have a child to look after means you will be more tired than the last time you were pregnant.
Maybe try sorting out a 'date night' once a week, where you make sure you either go out for dinner, or cook something nice at home, make sure the TV stays off and just spend some quality time together (this works well after babies are born too) chances are it will lead to sex, but even if it doesnt, it is good for your relationship to have the opportunity to discuss any issues that either of you may have in a nice calm environment or simply just to catch up with each other at the end of a busy week. It keept that emotional closeness even if the physical side is lacking a little.