D.C.
Please get him back to a Dr. if you think he is having trouble breathing! Go when the baby is hungry and feed him right there in front of the Dr. and show him what's happening.
Some other ideas: You have a fast/forceful letdown. Make sure he is not laying down and nursing, but try to keep him verticle so that gravity isn't causing the milk to come out even faster. Please check out this website and see if it describes your baby: <http://www.kellymom.com/bf/supply/fast-letdown.html>. If you are pumping and feeding from bottles, make sure you are using very slow nipples, or even try a different bottle type with a slower nipple and again, make sure he's not lying down to drink from the bottle.
Another clue is the green diaper. There are 2 classic causes for this. You have an oversupply problem (this often goes hand-in-hand with the fast letdown of milk), and your baby is getting all foremilk and not hindmilk. The imbalance can cause a lot of gas, causing agitation, etc. The kellymom.com site above has tips for this too.
A second cause of green diapers is a food allergy - often dairy. Try cutting milk products out of your diet and see if that helps. A food allergy can go hand-in-hand with reflux, which several others have mentioned.
Really sounds like a forceful letdown/oversupply issue to me. If you want personal tips on this, message me.