Hello! Nice work with your sketchbook so far 
If i may offer a criticism and suggestion, it would be to work more on anatomical structure. In the last drawing, if you were to analyse the tridimensional structure, the symmetry of is not accurately observed, the right ear would be a lot more visible, and the right eye doesn't quite fit the skull (and both eyes look very close together). Her neck is also a bit thick.
I recommend drawing a bunch of human skulls for practice. This will help you draw heads better, obviously, but also help with general 3d forms.