Baby cries after bottle?

I know the obvious reason for a baby to cry after a bottle is because she is still hungry. But, could anything else cause this? I recently moved my daughter up to 6 ounces of formula, she took 5 for about a week, and 4 for about a month. Now, she's crying every time she finishes a bottle. She already gets 6 ounces every 4.5-5 hours, which is more than her pediatrician recommends, but I'm going to feed my child when I know she's hungry. She has severe reflux, she's only 10.5 pounds at almost 4 months. So, I'm worried that anymore food will make it worse. Have any of you experienced this with your little ones, and it be something other than hunger? She gets her 4 months shots October 2nd, so I plan to discuss this with her doctor then, but in the meantime, I don't want to be starving my child! Help!