Re: Emotional - not sure if 3 wk old is getting/gaining enou
If you can easily pump 100 ml (around 3.4 oz, non-metric LLLadies), then there's clearly nothing wrong with supply.
But your baby's weight gain does sound a bit low. A baby should regain birthweight by 2 weeks, and after that Kellymom.com (http://kellymom.com/bf/normal/weight-gain/) says that in the 0-4 month range babies typically gain between 5-7 oz (141.7-198.5 g) per week.
I think the pumping sounds like it is a good idea at this time. Hopefully it is a very temporary measure, something you do while you're waiting for your child to grow a bit and become a better, stronger nurser who can drain the breast more thoroughly. There's nothing wrong with him "not emptying" the breast, though- because milk is always being made, most moms find that they can express some milk even after a good feeding.
You might want to try a technique called "finish at the breast". Instead of allowing the feeding to conclude with the bottle, which hypothetically teaches a baby to associate the feeling of fullness and relaxation with the bottle rather than the breast, you nurse for a while, offer a supplement, and then put the baby back on the breast for unlimited time. That way the baby gets the idea in his head that bottles aren't how feedings end- they're a pause in between sessions at the breast. Hopefully this reduces the chances of the baby developing a bottle preference.
Definitely go in for frequent weight checks, and make sure that whoever is weighing your baby is following proper technique by weighing the baby on the same scale every time, and in the nude or in a clean, dry diaper. Since it's only a few grams of difference between normal weight gain and insufficient weight gain, and a full diaper or even a little baby outfit can easily throw off the calculation from one weigh-in to the next.
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