If you have fine hair that's prone to getting oily, you just might not be able to co-wash or no-poo. You might need stronger low-poos instead -- I've been hearing good things about the CHS Treatment shampoo, it's supposed to be gentle yet strong enough to remove build-up. It also contains protein, maybe that would be a good option for you
Many fine-haired curlies simply can't co-wash, and if they can, they still need to rotate in a low-poo as well. It seems for fine hair, conditioner only might be adding too much moisture to the hair and isn't strong enough to remove its own build-up, while on coarse/dry hair this isn't as big of a deal.