Breastfeeding is good for both the mother AND the child. It is THE recommended infant food by WHO, as well as MOH here. And I sincerely do not believe it has anything to do with lowered interest in having sex. Most likely, on the male side, not in mood due to work/stress/same-old-same-old in bed all the time/etc; female side due to work/stress/baby/family/friend/household/same-old-same-old in bed all the time/etc. It's something that does not really come into the picture 'right after marriage' and 'before giving birth'. It's the adjustment both sides need to do in order to get back to the once 'romantic newly wed' mood that's difficult.

Lots of tips to be found via your good ol' GOOGLE. Go look it up.