With my last pg, I didn't start gaining any weight really till nearly 20wks. I only put on 15-17kg for the entire pg, which isn't a lot at all for me - the other three were all 20kg plus. Up till the 20wks mark I'd have been lucky to have gained 2kg. Not that I minded at all LOL. But I did have worse morning sickness than I did for the other three and wasn't eating much even though I did have a big bump by then.