First of all, stop beating yourself up. Seriously. It's annoying.
Next, to your actual drawings. All of them seem to have extremely gaunt cheeks; from the side of their eyes to their chin is a diagonal line. That's really odd looking. Also, their necks are giraffish.. really thin and really long. Slim is one thing, but those twigs couldn't hold up a head any day. Speaking of slim, from what I can see in your pictures, all these girls have incredibly hourglass figures. It's a little too exaggerated.
Onto your strong points. I like the way you draw your eyes, they really stand out and show the person's emotion. Also, the way you ruffle their shirts looks pretty neat.
I hope you understood my criticism and will continue making more.