hey dude, i think you should put photoshop away for a few months and just be focused on drawing ! as you know, you still have some difficulties with that, and a good painting cannot be without a good drawing underneath, so keep drawing as much as you can, just fill 2-3 sketchbook from life, also, you should start to study anatomy through loomis' books ( pdf available everywhere on internet for free, called " drawing for all it's worth " ) or bridgman ( really cheap books on amazon ) !! anatomy takes years to master, so the sooner you start it, the sooner you master it !! keep it up !!
Hey man, just be a little more patient with your studies. It will pay off eventually.
Try imagining what ever it is your drawing as simple shapes (cubes, sphere, cylinders), it will help you avoid the flatness in your drawings.