Hi Isle - we also just dropped the DF for our little Molly.
Are you breastfeeding? Sometimes breastfed babies need to eat more often than bottle fed so I don't have much experience in that regard. Sorry.
When your DS wakes do you automatically go in and feed him? Have to tried to just leave him to settle himself? If that doesn't work, have you tried going in and resettling without feeding? I would imagine at that age he may still need one feeding in the middle of the night, but not more than that??
The one thing I noticed with Molly and her night wakings is if I keep her evening activity to a very minimum she sleeps way better at night with less wakings. I was playing with her in the evenings, having her practice her rolling, sitting up etc. and she was waking every hour! Then I started just having her sit in her chair, talking to her, not much "practicing" of anything and she seemed to settle better at night.
Maybe give that a go and see if it works?? I have heard that at this age 4-5 months their nights are full of wakings due to all the new things they are learning. It does pass though and soon you will get a whole night sleep!!
