My 6 month old baby girl put on 100g from her 4 month weight. She fell from above 50th percentile to 25th percentile. She is fully breastfed latching on demand. Should I be worried?

Unless your baby is malnutritioned, you don't have to be too worried about growth charts. There will always be people on either end of the chart. You may want to consume foods high in healthy fats to increase the fat content in your breastmilk. http://www.webmd.com/diet/ss/slideshow-healthy-fat-foods