My baby is 9 mos. old and throws up after drinking juice, her formula and water. She doesn't throw up food. ?

I still burp her because sometimes she doesn't. I feed her in an upright position and when she sleeps, her head is raised. She eats about every three hours. The doctors keep telling me it's common and by her first birthday she should be over it. There is lots of phlegm mixed in with it. She's gaining weight so there is no problem there. She's very active.This has been going on since she was a newborn. She was fed and threw up the milk also. I usually let her tell me when she's hungry, I was afraid I was over feeding her.