Did you have over supply? Often over supply leads to babies getting lots of milk, but as mum makes so much milk the fat tends to get reabsorbed into the breast tissue as the milk waits to be consumed (or that's how I understand it, anyway.)
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What were baby's symptoms? Did your DS not gain weight? Have frothy green poops?
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Fortunately there are some really good ways to rectify this situation. I had a MASSIVE oversupply with my DS, and I ended up block-feeding in 10 hour blocks, and also feeding reclined with baby sitting upright, and a bunch of other things. Fortunately I got it under control and we are still going strong at 10 months! 
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Here is the link that helped me. http://www.kellymom.com/bf/supply/fast-letdown.html
and this was interesting too http://breastfeeding.hypermart.net/toomuchmilk.html
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It would be helpful if you could describe the situation, how you were told you didn't have enough fat, how baby was nursing, what you tried that didn't work, what lead you to give formula etc that would be really helpful and the Mamas here will be able to give you even more detailed suggestions.
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ps Congratulations on your pregnancy
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for getting as much info as you can before the cutie-pie arrives.