Underweight 8 month old

My daughter will be 8 months this week and is still under 14lbs. She’s happy, she pees and poops regularly and nurses on demand and sleeps well. She is developmentally on track. Sitting, crawling, pulling to stand, and starting to use furniture to cruise. She even says dada and can sign for milk. So she doesn’t seem to be too affected. The doctor is aware she’s dropped percentiles and I’m going in every 6 weeks to check her weight. We have been feeding her more and waking twice during the night to nurse and she gets 3 meals a day on top of that. She’s very active and I think that’s why she doesn’t gain. I’m SO stressed about it still. I’m wondering what they’ll do next week when I go in because I just weighed her at home and she’s still 13lbs 10oz. She will not take a bottle, so formula and my excess stash of Breastmilk is no good. I have to rely on nursing her. Anyone else been in this position before?