Hi lolly, I don't know anything about the weight thing, but the MW will keep an eye on you and bump and will say if she's concerned. When I was full term ppl thought my bump looked small yet Nancy weighed 7lbs 10oz!
Why not try swapping your folic acid for a multi vitamin for pregnant and breastfeeding women. I took 'Sanatogen pro-natal' because I was worried I wasn't getting a very varied diet (too busy!!) it's got calcium in it, although I really didn't need that coz I craved milk - I usually can't stand the stuff!!
I hope you feel less sick soon, good luck!
k8.x