Acne.org Products
My face from my eyes to my jawline has been itchy. My dentist recommended Sensodyne Repair & Protect. Brush for 2 mins with Sensodyne Repair & Protect, then apply a little extra with your finger on the other uncomfortable areas on the inside of your mouth, and voila. My face is not itchy anymore. Maybe you can try it with any toothpaste. I knew about Sensodyne before, but maybe I misunderstood what sensitive teeth felt like. I still dont think my teeth feel sensetive, more like itchy gums, but either way Sensodyne Repair & Protect relieves my itchiness 
Ive also been told to use Colgate Fluorigard, I started using it at the same time as Sensodyne, but of the two the Sensodyne feels more affective.
I think youre right to go natural with less chemicals. I dont use external acne products, I just shower and use some regular facewipes. If youre having problems you should certainly think about oral care, you might want to consult your dentist first, but the products Ive mentioned are available without prescription and popular in the UK anyway.
Regarding timescale I have noticed immediate results and Im feeling better everyday. Regarding directions for use: I was instructed to use my regular mouthwash before I brush so it doesnt wash away the Sensodyne when I apply it. I also use Fluorigard seperately to brushing, usually before bed, so it doesnt wash away the Sensodyne.