I have been exclusively breastfeeding my 4-months-old daughter and after a few initial difficulties (slow weight gain, latching problems/sore nipples, thrush), we finally settled into a nice rhythm. She was 7 lbs and 14 oz at birth and weighed 12 lbs by the time she was about 12 weeks old. Around that time, she suddenly seemed to go on a "partial nursing strike." Her nursing sessions were always relatively short, but suddenly she did not want to nurse more than 3-4 minutes on each side (expect for a couple of times a day, when she goes for about 15 minutes total). Since that time, she hasn't gained any weight at all. She sometimes gains a couple of ounces over 12 lbs, but then loses a couple of ounces, so she's been around 12 lbs for the last six weeks.
I really don't know what to do! She was diagnosed with reflux, but she's been on medication and seemed to be doing fine with it. I nurse her on demand (around 10 times a day), I don't restrict our nursing sessions, I've cut dairy from my diet, tried multiple nursing positions, nursed at night, in a quiet room, etc. I just don't know how I can make her nurse longer.
She's a very happy baby other than the lack of weight gain. She's meeting all her milestones, maybe even a bit on the early side. She's not sick, but frequently has greenish mucous in her stool.
I've also never used a pacifier or anything else that might interfere with her nursing. We've only recently started giving her a bottle of breastmilk every evening because she just doesn't seem to eat enough.
Do any of you have any ideas what might be happening? She was initially in the 20th percentile for weight, then went up to the 40th, and now she's in the 5th-10th percentile.