Congrats!!!!
Are you pumping with a hospital grade breast pump after each feeding?
You need to empty your breasts to keep that really full feeling.
Pretty much engorgement right away means it all kicked in. How do you know you don't make enough for a full feeding?
10 day olds don't eat too much, so maybe your body is regulating itself?
Best way to tell if the kid is getting a few ounces into them (especially if pumping gives you very little milk):
weigh them with a fish scale. You can zero the scale with a sling, and put the baby in the sling to track the ounces gained before and after feeding. Weighing the baby like this made me feel a LOT better about my nursing. We also ended up supplementing with an organic milk-based formula, but she was nursed 5-10 times a day once I started back to work full time (weekends were full time nursing), with one of her weekday bottles being pumped at work from the day before (and now she's 2.5 and still won't wean properly from the breast, it's kinda annoying!)
I did weigh her this way all the time when my baby was tiny because I had some serious milk issues. Mine never came in properly until I took reglan and domperidone. I tried everything "natural" first, but nothing happened with all the herbs in the world (I smelled like maple syrup for days from drinking all that tea and taking all that fenugreek.)