I didn't get weighed in my first pregnancy after the booking-in. With this one I was concerned about weight loss as between getting pregnant and booking-in I'd lost 4-5lb. It wasn't through sickness, I believe it's due to breastfeeding my one year old, and I don't want to stop. I mentioned it to the midwife and she's written it down that I'm to be weighed at my next appointment to monitor it. I've been weighing myself at home too and thankfully not lost any more, although I'm much earlier on than you are.
She suggested really taking a look at my protein (I'm a vegetarian so it's slightly harder) and having a hot chocolate made with milk at night to replace some of the calories lost through sustaining a pregnancy (and BFing in my case).