My hair did that after I gave birth. It was a patch near the back of my head. That's why I went natural. Maybe you're allergic to a product you're using. My hair stopped liking relaxers.
Shampoo: Terressetials Mud Wash (lavender or lemon)
Co-Wash: Trader Joe's Tea Tree Conditioner
Deep Conditioner: Anita Grant's Rhassoul Deep Condish
Leave In: Kinky Curly Knot Today
Creams/Oils: Raw Shea Butter, Extra Virgin Coconut Oil, Extra Virgin Olive Oil, Jamican Black Castor Oil and Jojoba Oil