Try a dilute vinegar rinse and/ or protein treatment. I would not use any penetrating oils, that will potentially lock in the hair colour, oils don't moisturise anyway they are anti humectants. Try soaking your hair in the Head & Shoulders not just washing it. If that does not work you may have to suck up having bad hair for a few weeks.
2a-2c, medium texture, porous/ colour treated. Three years CG. Past bra strap length heading for waist.

CO-wash: Inecto coconut/ Elvive Volume Collagen
Treatments: Komaza Care Matani, coconut/ sweet almond/ fractionated coconut oils, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss Ultimate Volume, various Elvive
Styler: Umberto Giannini jelly, Au Naturale styling gelee
Flour sack towel, pixie diffuse or air dry.
Experimenting with: benign neglect