Sorry you aren't feeling good, mama
I lost a few pounds (8ish) in less than a week during the first trimester due to hyperemesis. While in hospital for fluids, I saw the nutritionist. After a few minutes of really unhelpful conversation ("Are you eating enough??" Ummm... no. Anything that touches my lips including water gets thrown up. "So I see in your chart that you are a vegetarian. Are you getting enough protein?" Ummm... no. I throw that up too.) she did have a few good pointers. I probably would have done some of them on my own anyways
if I was actually able to keep anything down
: , but I'll give the nutritionist some credit
Three things that helped me start regaining the weight after the vomiting was better controlled were:
1.)eating
all the time
2.)eating things that were very dense in calories/fat/protein like nuts or avocado or a really dense bread with nut butter (I liked cashew a lot)
3.) always keeping something to eat in the car and in my purse
My doctor says that most of the time she doesn't really care about these silly weight gain formulas as long as you are eating healthfully and the baby is measuring at a good size. So you might not need to worry about it too much as long as you don't keep losing weight and the overall trend over a few weeks is ok.
Of course there are situations where you have to get right on top of it- it would make sense that twins could be one of those times.
I wish you a healthy pregnancy and chubby babies!