Hi, I've never posted here before, but I wanted to share what has worked for me.
I'm 34 years old, female, and have had acne since I was 13, mainly cystic around my jawline. I had tried almost everything short of Accutane; including birth control pills, antibiotics, benzoyl peroxide, topical retinoids, B5 megadosing, Korean madecassol ointment, urine on my face...that's all I can think of right now, but the list goes on.
My skin is not completely clear as I get the occasional tiny whitehead and still have red marks from old cysts. But it's completely smooth, even if the tone is somewhat uneven. It was they cystic bumps that caused the most angst for me.
I cut gluten out of my diet and that made a big difference, though I didn't get completely clear. Stopping hairspray use also went a way in making my skin better.
It was when I switched my foundation to Invisible Zinc that my cysts stopped completely.
It may be the combination of the zinc and the lack of gluten, because when I accidentally eat gluten a couple of days later I will get a little breakout, though with the zinc foundation it is much smaller than the old days and clears up much faster.
So it's worth a try. You could probably find some clear zinc solution if you don't want to look like you're wearing foundation. I use Invisible Zinc UV Silk Shield Foundation. I'm not sure if it's available outside of Australia, but with ebay etc that's moot.
ETA: I've been gluten free for about 2 years, and I've been using the zinc foundation for about 1 year.
Invisible Zinc is the brand name, it's an Australian company. Usually I find it at the pharmacy (drugstore) or at Priceline, on the same shelf as sun protection.
If you can't find somewhere that will post it to you, there would probably be a similar product you could try. I know nappy rash ointment has a high concentration of zinc in it. I tried that for a while, but the one I bought also had cod liver oil, and the smell was so fishy that I gave up wearing it on my face (also it was very white so I could only wear it while I slept).
You could also just look for clear zinc in the sun protection aisle, it's the only sun protection I can wear without breaking out; you could wear it all the time and see if it helps your skin. At the very least it will help prevent wrinkles 
Yes, yes, yes! zinc oxide is amazing. I bought a one pound bag of pure zinc oxide and mix with jojoba or coconut oil and apply every other night to my face, alternating with tretinoin and my stubborn chin, jawline and neck cystic acne is totally under control and I'm 100% clear including no plugs that turn into acne later. It also helps heal active breakouts as well as prevents and lessens scarring AND is vital for new cell growth including collagen.