Every single women is different. It is common to gain some weight at first. Your blood supply increases, your amniotic levels rise to cushion baby and a lot of other factors cause first trimester weight gain. However, with morning sickness it is also common to lose some weight at first since a lot of women experience nausea and poor appetite. Don't worry and Congrats:)
I did gain some weight, more like 5 pounds. My doctor was really upset, actually every time I go she makes me feel so bad because she says I gained way too much in a month's time.
Anyway, as long as you feel ok and healthy and stay active (basic!), you are good.