My story is very similar to yours, except my PD persisted for 3 years! I'd have a breakout every 3-4 months (that only responded to Doxycycline, but it would always return.) I was at a loss all that time because everything I used on my body was as near to homemade as possible and I put very few, if any, unnatural substances on my body. My diet is much healthier than most as well.
Well, pure serendipity brought me to a dermatologist with a personal opinion... "Stop with the coconut oil already! " I made my own toothpaste with it, my bar soap had it as it's second ingredient, my moisturizer was pure coconut oil, and I took 1tbsp of it each day in my coffee. It's then that I realized that PD started shortly after switching to pure coconut oil for my face moisturizer.
What?????!!! So simple yet I overlooked it because I thought, "it's natural and unrefined. It couldn't be that."
I was wrong.