I don't know what products are available to you, but a few general ideas that might help:
Have you figured out your hair's properties (texture, porosity, etc)? These make a huge difference in finding the right products.
Make sure that when you co-wash you're massaging your scalp very well (I usually do a good 2-3 minutes). And continue to massage scalp as you rinse.
You might want to try rotating in a sulfate-free shampoo (low-poo). There are lots of people who cannot co-wash exclusively, especially if your hair is fine in texture.
Have you tried baking soda or an apple cider vinegar rinse?
I hope this helps a bit.
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3a/f/iii Before the chop- Donated to Locks of Love, January 2013
Modified CG since 11/5/11
CO-WASH: VO5 Vanilla Mint Tea Clarifying, DevaCare No-Poo
CLARIFY: CHS Treatment Shampoo (used prior to PT/DT)
RO: DevaCare One Condition, Regis Olive Oil
LI: Cure Care, As I Am Leave-In
STYLE: Re:Coil, Curl Keeper, Biotera Gel, Deva Ultra Defining Gel, GVP Liquid Sculpting Gel, Curls Rock Amplifier and Strong Hold Mousse
PT/DT: IAGirl's PT, One n' Only Argan Hydrating Mask