For your back under neck middle: Don't know the type of soap that you use in that area now.
Have you tried a more neutral soap with least amount of fragrance and least amount of cream inside soap? ie. By Neutrogena or Allenbury.
Don't scrub too hard that you might create open sores and hence, cause more infection. Everything you wear before, during and after cycling must be clean in your tops for next few weeks.
Is your hair long at the back ie. below the nape of your neck? I used to have this problem as a teenager when my oil glands would more active plus I had long hair past my shoulders. Another reason why I had to have a haircut that lifted all of my hair away from my back/neck area, to control/reduce breakouts.