I've been struggling with acne for almost 4 years now (I'm 16). I feel like I've tried everything to cure it and nothing seems to work. I've been to the dermatologist multiple times and every time I go they give me new topicle medications and pills nothing from them has worked. I haven't been back to the derm. for almost a year. My acne is mainly all over my back and a little on my chest. My skin is so stubborn nothing helps it. Since not using any of the medications from the doctor I have been researching home remedies.
I have tried:
Tea Tree Oil
Coconut Oil
Tea tree oil and Coconut oil together. Really cleared up my acne for a little while but stopped working after a couple months.'
Lemon and Sugar
Epsom Salt
Benzoyl Peroxide 10% body wash
Switched to bar soaps to wash my body
I wear shirts only once
LUSH Fresh Farmacy bar soap

I do not know why nothing seems to be working.. I feel like I'm doing everything right. I am really active, I play 2 sports and I eat as healthy as I can. I take showers everyday and right after being really sweaty. Also I cut dairy out of my diet right before school started this year. It seemed to improve my back acne a lot but as soon as school started (a week or two later) my face broke out so bad. I have never had acne on my face before, normally just 1-3 pimples on my face but now its all over my forehead. I don't know what to do.. Could the stress of school be causing my face acne? Also my face is super oily also, but oily and dry on my pimples in the fall and winter.
And now after not having dairy (milk, cheese, ice cream ect..) for almost two months, I just have been getting huge, painful pimples on my back and a lot of super tiny ones. And I have never scared before and now I have been getting these pimples that when I pop them the only thing that comes out is puss and blood, and It leaves a little hole and later scares. I do not know why this is happening! I have never had this before.

Please comment your suggestions on what I should do! It is something I am eating? Or my lifestyle? Is there something I should be putting on my back?
Help I need answers! I want this acne to go away!