My twin girls were born 16 days ago at 31 weeks 3 days and are in the NICU, where they'll be for quite a while yet since they are so little and early. I'm pumping and working on building up my milk supply, because once they can eat I'm going to have to produce enough to feed two babies.

Up until now weight was coming off me really quickly, but it seems to be stalling out. I started eating a little more because I was so exhausted, and eating more seems to help and seems to help my milk production too. So my question is, how do I figure out how much to eat so that I can keep increasing production but also lose weight?

First congrats on your twins!! I am not due until the beginning of August but I need to research the same thing. I wanted to breastfeed my first son but stopped at like 2 weeks. Even in those 2 weeks I was using formula (reason I never built my supply).
With my second son I did not diet (and did not lose any weight) until after I weaned him.
I don't want to wait 6 months this time to start weightloss, but I've been curious about that same issue, dieting and not being able to build a good milk supply. And you obviously need to really build up your supply!

If I had to make a guess (and I haven't confirmed this) I would say that if you are counting calories to try changing the number each day. Like 1500 one day, 1700, the next, 1600 then next, then 2000, then 1500. Also I woud say that what you eat would be extremely important. I would think that foods very high in protien and healthy fats would be most important. Now is probably not the time to use a few hundred calories on a serving of chips lol.
You did say the weight was coming off, then stopped when you increased your food intake. You could try dieting for a bit (which you did) then giving yourself a break (which you are) then maybe a week or two later diet again, then after a week or two, a break. ...I know that's not ideal...or you can just monitor your supply. If you see it going down increase you intake for a little while, until your supply goes up, then slowly decrease your intake. I think the idea is trying to find a balance between a slow weight loss without having your milk supply suffer.

I know with my second son, it took about 6-8 weeks to build my supply to where it was too much! But that was nice to, because I could freeze it and then my husband could feed the baby and it gave me more freedom. However, those first 2 months, I swear I feed him every 10 minutes!!
Good luck!

Not sure if this helps as I don't have twins....

I have been dieting hardcore now for about 1 1/2 months. I had my 2nd daughter in Nov, but couldn't exercise for a few months afterwards due to a prolapse. (Fun times!) Once I could finally start exercising, I cut my calories to 2000. I was so afraid of my supply being too low. But eventually I started cutting back more, and now I try to average about 1600 calories a day, while also exercising (usually running about 20-30 minutes a day). I have been steadily losing about 4 pounds each week since I started. I haven't had any problems with my milksupply, and my little one eats ALL THE TIME.

I would also suggest Mother's Milk tea -- seriously one cup of that stuff and I am leaking out nonstop. I bought in just in case my supply decreased, and it is amazing. Literally one cup, and then I am a fountain. I know there are also fenugreek supplements you can buy (same herb that is in the tea), that is supposed to do the same thing.

Congrats on your twins!!!