Not gaining weight

I’ll be 18 weeks tomorrow and I haven’t gained much weight. Is this normal? In the beginning I lost about 7-10lbs. I was at like 154 lbs and then dropped to 147 at my lowest and now I’m at 150 but have stayed at 150 for several weeks now. The doctor said I should gain about .5 lbs a week and then after about 1lb a week. I just hope the baby is growing and getting enough of what she needs.