I would like to also recommend try pumping, and if he still doesnt get full then you may have to switch to baby formula. I was always told to do that for when I get pregnant.
Congrats on your baby and hope you find out what you need to.
Also there is a breastfeeding forum, they can give u lots of great tips.
debay, you need to consult the hospital where you delivered your son for help. They've got lactation consultants, you can come in and feed him and have him weight before/after feeding with very sensitive scales to make sure he's getting enough.
You're right to be concerned, and because you're a good mom you're following up on your questions and hunches.
Most women can successfully breastfeed, but many can't, and you're wise not to let this get to a crisis situation before you get the answers you need. Just call the nurses desk at your hospital.
Best wishes, and congratulations on your new baby!