I've been a postpartum nurse for seven years, and I still enjoy what I do. As others have said, some of the stuff gets repetitive, but you're going to find that no matter where you work. When you teach about the same conditions over and over again, that just happens.
What changes is the babies and the set of challenges each couplet and family faces.
As fiveoffive mentioned, many moms have health problems that affect their wee ones. In a large urban hospital, you can expect to see a fair number of kiddos withdrawing from all kinds of substances, those who have blood sugar issues (r/t maternal obesity), and some who have problems like cleft lip/palate or other difficulties that require extra care but not necessarily a stay in the NICU. The abstinence babies usually end up in the NICU, but they most often start out in a regular nursery because it can take 24-72 hours for them to become symptomatic enough to require meds and closer monitoring.
Breastfeeding assistance is really important, especially on noc shift when the L'Cs are all snug in their beds. Your lactation training should prove a valuable asset to your patients and to your co-workers.
Very young moms, moms who don't speak English, crunchy moms who view anything medical with great suspicion, moms with numerous social problems and complicated family situations keep the job from becoming boring. There's always something going on.
As for working nights, I greatly prefer it. We don't have all the extra support staff (HUCs, PCAs, social workers, L/Cs, etc.), but we also don't have all the traffic of days and PMs. We're a closer knit group, because all we have is each other. We bring in food and help each other out far more than the other shifts do.
On the personal side, working nights isn't for everyone. DH is also on third shift, so we're on the same schedule, and that has been great. I'm a night owl by nature, and we've trained friends and family not to call us during certain hours. On our off days, we sleep from 0400 to 1200, so it's only half a shift difference. We can still plan appointments and other engagements for afternoon hours. The biggest thing is that you have to develop an attitude that you'll do what it takes to make noc shift function for you. If you resent it or fear it, the negativity will sabotage your efforts.
You sound like a good candidate for this kind of job. I hope it all comes together for you.