Baby cries after feeding?

i cant figure out whats wrong with my baby. she cries after every feeding. i feed her, and i know for a fact that shes getting enough milk. she seems to want to keep sucking but cries when she starts. ive tried everything- pacifiers, bottle feeding, rocking her, burping her etc. she kinda seems either extremely fustrated or in pain. i took her to the doctor and the dr said that she just wants to cry. i dont believe that. im so exhausted and i feel completely helpless. she will eat for like 20-30 minutes and then start to fall asleep, but then she'll wake up and start screaming and that lasts for like an hour or so.