I'm trying my moby with three-week-old dd and think I'm using it OK, but when she falls asleep her head tucks into her chest - how do I use it so this doesn't happen? When she's awake it's fine - I can see her face, can fit two fingers under her chin etc. But as soon as she falls asleep she looks like she's going to suffocate and I take her out - this is clearly not going to work outside the house unless I can get it sorted! Any tips please?