Well, as everyone has stated is the critique is very important, and they already put their input in, so here's what I have to say, the second drawing you did was a lot better than the first one, even in small details, though he had the head of a freakin' watermelon, haha, but in seriousness, you did fix proportions a little bit in the third drawing posted. I think you're progressively improving, but at a slow rate. You don't always have to understand how the body works, but it does help a lot, trust me, I draw like you, where I don't take into account anything other than "I'm going to start it, and I'm just going to draw everything in", but that took a LOT of time, and a LOT of practice, and I still find it a lot easier to start yourself with some guidelines of what position the character will be in, the proportions, etc.
It's important to take critique, and don't let anyone bring you down, keep at it, and you'll be fine. Best of luck to you.