probably when you breastfeed, hubby wont be touching your breast... can be several reasons.

1. when pressing (force), the milk might come out, thus causing some inconvenience during sex time.
2. when boob become soft, probably the husband just touching it without sucking it.
3. hubby think the breast for son/daughter food, thus dont want to mess it up.

other reason probably due to hubby, he might want to have quickie - fast do and sleep.