Trouble gaining weight

I can’t believe I’m having this issue. For the last 4-5 years I’ve been minimally OVERweight. In my first trimester I lost weight due to morning sickness, and my doctor is now concerned I’m not catching up fast enough. She says I’m around 10 pounds behind. I eat when I’m hungry. The problem is that that isn’t very often. I wouldn’t be concerned except that one of the twins is measuring quite small. That is why my doctor mentioned my weight at all. Aside from drinking supplement drinks does anyone have any suggestions?