Sounds like you are producing plenty of milk. I suggest giving your baby more time at the breast, not less. I don't think that the burning calories comment makes sense, either. My babies were small, jaundiced, sleepy, and inefficient (and below their birth weight at 3 weeks!). It took them much, much longer than 15-30 minutes to get what they needed! They ate almost constantly, sometimes taking turns and sometimes together, for the first couple of months. They needed the practice. Not until 3 months were they able to eat for 15 minutes and get what they needed. If I were you, I would offer the breast every hour during the day and allow her to suck until she stopped on her own. This might mean nursing sessions lasting hours, but that's just part of establishing breastfeeding. Right now it seems like a lot, and I know you're sad about missing out on other things, but in a few short months you'll be out with your family and your baby will be hungry and you'll be able to just feed her and then go about your day without bottles or formula. It's wonderful and satisfying and allows you to carry on with life in a very freeing way.
Like elliesmommy, we supplemented some in the beginning, too, and went on to exclusively breastfeed. So don't lose hope just yet!