Hi ladies. It's hard to believe your OVER feeding. I think "we" were overfeeding Amelia thanks to the Docs wanting us to get her weight up. They asked we feed her AT LEAST an ounce on top of what she was getting from the breast. As the end of last week came up, Amelia was at the breast attaching SO much better and after every ounce of formula supplementation, she'd throw up horribly. Now THAT to me is over-feeding. So we pushed things back and started supplementing only a half ounce on top of what she's been getting and letting her bf'd on demand.
NOW, my thought on your bf'ing issues. If your only bf'ing 15-30 min's on one boob and switching, your babies may not be getting that HIND MILK. It's the thicker of the milk and makes them full. If you switch too soon to the other boob, their getting the thinner milk and sometimes they can get gas just from taking that. Try bf'ing at night on ONE boob for awhile and see how the babies do.
Another thought is that you may not have a good milk supply. Someone told me that if your babies have to continue for a long period of time, they may not be getting the supply they need and that can be a sign. In which case you'd have to supplement.
I'm by NO MEANS a pro at this and think that the bf'ing forum on bnb could help a whole lot more than me, but those were two things that came to my mind when you mentioned your issues.