spitting up.

My 6 week old does this thing once a day where she spits up almost her whole feeding. Before this happens she's extremely fussy like her tummy hurts. Makes terrible faces like it's gagging her and spits up small amounts. I try to make her wait 2 hours before feeding her again and she still spits up her whole feeding. After she does this she's seems like she feels better. I've talked to her pediatrician and she put her on Zantac but it's not helping. I hate seeing her in pain!