i know this is coming from me (lol) but its really important that you draw other things as well
basically by drawing other things such as environments or objects or get better as an artist and thus, your people will come way easier
When you draw other things you develop styles and habits (hopefully good ones) which then you apply back to your people.
Its great that you are getting more realistic you have become so much better
but i can tell you still struggle with people mainly because your quick sketches of people arent as good as your fully fleshed ones.
For a week just try learning something new like perspective and then draw some basic plants/objects/whatever the hell you want. Your learn new techniques and new skills which then you will apply to your people and they will look even better. You have the skills to draw other things. It might not be excellent at first but you definitely have enough ability to do it i promise.
^opinion
if you dont want to draw other things then here:
http://fineart.sk/photo-references/andr ... tomy-books
andrew loomis anatomy books he is one of the best people drawers ever
The best way to learn people imo is just to do quick 5-10 minute sketches of faces and peeps
I did that for faces. I literally have probably done over 100 pages of 5-10 minutes face sketches and im still not great. But it taught me a lot. By doing little sketches you learn/develop new things and then you apply them to your bigger piece.