Mommy to Maxwell 10-9-07 weaned with love (a party and a remote control monster truck) on his 4th birthday
My Boy 3-16-10
And my sweet pea Sam 2-12-11
Watch Your Language
My story (and I suspect many others) is similar to yours...baby wasn't gaining weight like she "should" so pedi recommended exactly what yours did - pumping and bottle feeding. She also suggested formula. I just wasn't comfortable with her advice...probably b/c I had read so much info on breastfeeding prior to baby's arrival that I knew that there were better solutions than to basically give up breastfeeding.
So instead of following her advice, I just spent the next 3 days feeding every 2 hours religiously and gave her more time on each breast. At the follow up weigh in, she had gained 3 ounces which was an ounce/day gain! Average is half ounce/day.
The following week, I had numerous doctor appointments every day that kept me away from home long periods of time and we ended up with several times a day where I was going 3 hours at a time between feedings. A week after that last weigh in, I had a lactation consult at pedi's office and as part of it, we weighed her again. She had only gained half an ounce in that week!!! I was so upset and again it was suggested I pump and bottlefeed. But after I fed her in the office, they weighed her again and she weighed 1.6 oz. more. So now we KNEW she was eating a reasonable amount which sort of made the pump and supplement advice useless.
I bought a pump on the way home that day b/c now I was getting stressed about the lack of weight gain. I should note that she was having plenty of poopy and wet diapers which is supposed to be a pretty reliable indicator of eating enough.
Since I still doubted the pedi's advice AND the advice that the lactation consultant I called gave me (same advice, pump and supplement) I held off on using the pump. I was just really frustrated that everyone wanted me to pump rather than give me constructive advice for helping me to continue with actual breastfeeding.
So I went back to feeding a lot more regularly (now that all my doctor's appointments were over and I was home all day I had the time to do so) and I started taking Fenugreek b/c I was pretty sure my right boob was an underachiever. LOL!
By her two week appointment which was 4 days after that last weigh in, she had gained 5 ounces. So we were back to over an ounce/day of weight gain. And by now she was almost back up to birthweight (about 2 ounces shy).
I am SO glad I didn't take their advice. I was pretty confident that the problem was just low supply and I knew that nursing her regularly would help with that. I also decided not to worry so much about the numbers and focus more on the fact that she was putting out a decent number of wet and poopy diapers.
My point is that I went through the same thing you did and I would second the advice you were given here to dump the pump right now and just focus on breastfeeding her as often as possible. Go hard core with nursing her every two hours at LEAST and really get that supply up. Some people even suggest a "nursing vacation" where you just lay in bed all day basically and feed, feed, feed her.