We need a "My hair won't naturally dread" support group!
I left mine to go natural for a year before backcombing and I had no real results. I used to wash with diluted dish soap every couple days. I'm sure if I had waited another year or so it would have worked out tho, I just have very silky hair that at the time was only to my shoulders.
You're definitely not alone but you are going to have to be a whole lot more patient. My back-combed dreads were pretty straggly at three weeks and didn't start looking like dreads for about 8 months.