It could be from morning sickness if you've been experiencing that. I am now 19 weeks and have only gained 1 pound through the entire process so far and they said it's perfectly fine. Just be sure that you are eating healthy and taking your vitamins and you and baby should be fine.
I lost 30 lbs with my first pregnancy (son) and ate all the time.I just cut out most cokes/ caffiene. I weighed 195 and got down to 164. My doc never blinked an eye, i was more worried than they were. They said if i wanted to gain weight to drink a milk shake every night before i went to bed, i did and i still lost weight lol. But they werent concerned. I gained 60 with my second pregnancy (daughter) and never ate, or when i did i threw it up 5 minutes later. Now with this one i am 10 weeks and have lost ten pounds. And i am always hungry. My doc just laughed and said this one must be a boy too lol. So you are fine. Doc will tell you if they get concerned. And some girls on here i read lost lije 15 pounds in first 20 weeks but then gained 30 back by the time they gave birth