Don't worry about it- as long as you are getting all your nutritional requirements, evrythying will be fine- alot of women actually loose weight in the first three months, from having morning sickness, and no appitite, or not being able to keep anything down.
The baby takes what it needs from you, and you get the left overs !!!!!
Actually-come to think of it children continue to do that for their whole lives !!!!!!!!