Hey nice job on keeping a sketchbook. My suggestion would be to draw a little larger and to practice your figures as structural drawings showing perspective. Then you can start adding details. Also, when drawing the head from a profile, instead of a circle, it should be more of an egg shape. I did some sketches from some of your drawings to show you what I mean, I hope it helps :)

I think the only way to push through stagnation is to keep going. Draw what you think is cool and don't stop. You look like you're having fun with these, keep it up :)