wow you've made some amazing progress since you started this!
I agree with the previous comments, you should definitely do some anatomy studies, it'll really help you out. have a look at books by andrew loomis (out of print, get it online), bridgman, or hogarth. They also deal a lot with volumes, i.e. constructing your drawings properly out of 3d shapes rather than tracing outlines. it helped me heaps
I'm not sure I'd get into PS so early, for two reasons:
1 - it has an undo button. that thing is EVIL! traditional media are a lot less forgiving and help you learn from your mistakes rather than just undo them without consequences
2 - it has colour. at this point i reckon it's important for you to get your foundations right - proportions, shapes, volumes, silhouettes, line quality, value. once you got those down, jump back into PS and you'll find it much easier
that's what my mentor told me when I started drawing, and it worked. so I thought I'd pass it on