Sorry to hear you're battling this. We were in that boat too and its stressful. Of course Daniel was really growth restricted so it was one of the doctor's top concerns from the start. They added a teaspoon of Neosure powder (preemie formula) to every couple ounces of breast milk and we bottle fed him. So he was getting the benefits of breastmilk, but it was further concentrated with fat and calories by the Neosure. There was never any water or premade liquid formula added. And my son caught up like a champ, and then some in time. Are you doing this, or would this be an option?
You might ask your pediatrician if your milk can be analyzed. No biggie if not, but if your insurance covers it and the ped orders it, it's a nice to have nugget of information. They assumed I was pumping water while Daniel was in the NICU. He wasn't making progress for awhile and they were adding the neosure AND something called human milk fortifier to my breast milk. My test came back and it was the highest fat and calories the lactation consultant had ever tested, and she'd been there for over 25 years. I read something Dr. Sears wrote about how your body can know what your baby needs and produces it in your milk, sort of a perfect prescription for your baby. I guess it held true in this case.
Another thing... your baby hasn't been Earthside that long, and babies have growth spurts. He could be gearing up for one. It's good to pay attention and not get too far behind, but I hope you're not as neorotic about this as I was.
I know, easier said than done! I'll probably obsess over feedings with the next one too!