Has she been eating the usual amount Mel? It can be a bit tricky when they start sleeping too much and not eating enough then end up not having energy to eat properly and subsequently put on weight.

A friend's bub was fully BF'd, and was sleeping through the night (this is from birth and an extreme case) and in his first six weeks didn't put on any weight, can you imagine her shock! She hadn't realised, poor girl!

But I am sure it is just her recovering, how long ago was she sick and for how long, prob will take her a while to get going again

EDIT: Oh by the way - why are you a registered user and you have nearly 7000 posts!!!