I think the thing I'm seeing the most is proportional issues, which I think might be a result of your short pen strokes on those 30 sec to 2 or 5 minute drawings. The thing that a long line does is not just provide a more sweeping gesture, it also defines a lot of space at once. Using short strokes over and over takes a much longer time to define the same amount of area. What this does is, one those short-timed sessions, gives you less time to actually consider the form and how things are spaced.
My suggestion would be to take a few seconds just to consider the form, draw the head and the angle of the neck, then draw the largest defining curve you can find. Then stop. Consider the form again, the distance between that line and the next most defining curve. When you've determined the distance, draw that line and reconsider the form. It doesn't take as much time as you'd think, and it helps you consider the whole form rather than one particular area. In this way it may not only help with your overall proportions, but also with making the sketch feel more cohesive and composed.
If you haven't seen his stuff already, I draw heavily from the site Proko which has a lot of amazing drawing tutorials for free. The one I revisit when I'm having trouble with these kinds of things is his How to Draw Gesture - Step by Step tutorial. All of them are good though.
Congrats on the 2 year track record by the way! That's absolutely fantastic. Happy drawing!
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