You should be fine. Some loose it the beginning of their pregnancy and some gain it. But you'll gain weight as you get farther along. I'm 6 months 3 days and I barley gained 17 pounds. But at my 3 months I still hadnt gained anything..
I'm 29 weeks and haven't gained anything, actually lost some of my pre-pregnancy weight. But my baby is growing fine. With any concerns ask your OB /midwife.
You're not supposed to gain weight in your first trimester.
Unless you were underweight before pregnancy.