Hi Lily J
Don't worry at all. I'm not at 12 weeks yet (only in my 8th week) but I have actually lost 4 kgs. My dr said not to worry at all, and that as awful as it sounds, babies are the perfect parasite - they take what they need to grow - even if it's at your expense! That's how come even in developing countries babies are still born at an average weight of 7 pounds or so.
Just keep an eye on it and check in regularly with your ob. They'll tell you what you need to do.
x