How are you styling your hair? I've NEVER been tender-headed in my life until the last year when I started braiding my own hair (not tightly) in a few plaits beneath my wigs for 4-8 wks at a time. Whenever I'd take my braids down, my scalp was tender. I don't know if it's from growth (I take lots of vits, and use an MTG-like growth aid), or from my hair being tucked away with no manipulation.
Tea tree oil is very good for the scalp, but make sure you mix any EO with enough carrier oil (olive oil, coconut, avocado, castor, etc). because applying pure, concentrated EOs directly to skin is NEVER recommended. Since you mentioned the OO, I guess you are already using a carrier oil. It could be the growth that is beginning, idk you may not see it yet but since the follicle is beneath skin's surface, the oils/vits may be having an effect there, causing the soreness. Just a theory, but HTH!