Doc appointment rant?

I didn't gain the weight i was supposed to gain in fact i lost weight. Now I'm -9 of what i should be this month, which is pretty much over. The baby measured right on track but the doc who filled in for my regular doc wasnt worried at all. She also couldn't answer any of my questions and just said she have my doc call when she got back. :/ not helpful. BUT my doc said she wanted me back up to 1st month pregnancy weight which was 185 but I'm 164 now. How am i supposed to gain 21 lbs and still eat healthy and stay active??? I eat 3 meals and snack like 90% of the time?