I'm a name changing regular btw, until I have told RL about my BFP
Perhaps DS is just all partied out with Christmas etc, but he's been really sleepy and a bit grumpy for a couple of days now. Could it be the hormones in the milk? He is feeding a lot just now, even more than normal I would say.
I knew somebody who's toddler got morning sickness when she was pregnant (she had HG so the hormone levels must have been through the roof) but have never heard of tiredness and grumpiness being transmitted through milk
Of course, he might also be coming down with something