IMO your making it up as you go along...
...so what?
Well modelers tend not to do that - they use concept sketches and photographs on pretty much all organic models, it's the only way to work. Even the best character modeler couldn't make a character from scratch with no concept references. I think you'd be better off practicing from concepts, it's actually more fun to try and recreate something - because it's a great feeling of achievement and a good challenge to get it looking cool.
There's so many factors with character modeling to consider on top of just modeling - animation is a major concern because the areas around joints often need very special care otherwise limbs bend like cardboard tubes. Practice makes perfect, just keep at it.