M.K.
If she was eating tons and now is eating less, it may be possible that she is still hungry! Is she still eating the same but just less often? Some babies eat more often than others. Probably soon you'll start solids, and that might help her sleep better. My daughter cried herself to throwing up, so I know what you mean about the hysteria. If you keep things as soothing and calm/quiet as you can when she wakes, and only pick her up if you have to, that should help her stay drowsy. With her very early waking, it could just be how she is... try moving bedtime a little later in 5-10 minute increments to see if you can reprogram her waking time. Good luck!