Re: baby weight gain concerns
A stomach bug could definitely account for the lack of weight gain. Also, it's normal for growth to vary from month to month- some months your baby will put all his calories into height, other months he'll grow in weight, and when he gets mobile, he'll probably start putting a large proportion of his calories into motion. Growth isn't always a smooth curve like the ones on the charts.
So long as you are feeding on demand and your baby is making enough wet and dirty diapers, I don't think there's much cause for worry.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"