Problems with my *almost* 3 month old.?

My daughter will be 3 months on January 7th. She has been a "spitty baby" since birth, but I think it is more than that. My son (almost 3 now) had mild reflux and we chose not to medicate because it wasn't causing him discomfort. However my daughter seems to be in a great deal of pain/discomfort with her spitting up. She spits up LARGE amounts...not like a few table spoons, more like a few ounces at a time. We have tried Zantac and it made things worse. We have gone to the ER in fear of dehydration, they tested for Pyloric Stenosis- negative. Saw a public health nurse who said it was just reflux and to see the family doctor. Saw the doctor who says "maybe it is not reflux because the Zantac should have helped that". The doc thinks I am OVER FEEDING her. I feed for 10-20mins on one every 1.5-2hrs. I use the same a few times, then switch to the other for a few feedings (etc). The doctor suggested forcing her to wait longer between feedings, preferably AT LEAST 2 hrs but aim for 3. This is NOT working and I have stopped doing this and gone back to feeding when she wants (every 1.5-2hrs).Making her wait longer is like someone is torchering her, she just screams and screams no matter what you do to soothe her. The longer stretch between feedings didn't help the puking anyways. Even if she goes 5hrs (she does this once a day) between feedings while she sleeps it makes no difference. I have tried modifying my diet- no help. She is gaining weight OK, like the minimum amount she needs to gain, so my doctor says he isn't concerned. I understand that weight gain is important in making sure the baby is getting enough, but the only reason she is gaining is because I am almost constantly nursing her. Its a vicious cycle of nurse-puke-nurse-puke-etc. Sometimes she even eats twice an hour in the evenings. I am becoming exhausted. I am at a loss on how to break this cycle. Any similar experiences or advice?