3 months old not drinking milk

My baby is going 3 months. When she is awake she refused to drink and will keep crying. She only drinks when she is sleeping. But she can't possibly be drinking and sleeping during all her feeds as some will be in the afternoon where she will be awake. I am not sure what's wrong with her. What should I do? we tried all methods. Change diapers all that also no use. She did drink abit when we carry her and walk around but after maybe about 20ml she will start crying again. #advicepls