I can't co-wash exclusively. I had too much build up and realized co washing isn't for everyone. I have low porosity hair and hard water so co washing left my hair coated all the time. I use sulphate free poos every time I wash. I also do BS/ACV rinses about once a month and that really helps.

It could also be that you scalp is adjusting. I never had scalp issues per se. I have read about others on here that go through a yucky initial phase before scalp adjusts.
3a/b, fine texture, low porosity, normal elasticity, mod-CG 7/11/11

Poo: KC Come Clean, SM Moisture Retention
CO: CJ Curl Rehab, CJ Argan & Olive Oil, Renpure Argan Oil, YTCucumbers, Sevi Pumpkin
Style: AIF, HESMU, Biolage gelee, KCCC
LOOB for second day hair

Like BS/ACV rinses, limit protein/humectants.