Back acne!

Toothpaste! It is the best thing I have found to dry up a pimple!
If there is not a visible whitehead, you may want to take a hot bath or go in a sauna to draw it to the surface.
Sometimes I even poke the pimple with a (clean!) pin to open it up and drain it so that the toothpaste can really penetrate! It has to have a whitehead (looks ready to pop!) to do this though.
In the morning, wash the toothpaste off, and then apply moisturizer (non-comedogenic). You should have at least three full 24-hour periods before your wedding so that it can heal. You will likely still need to apply cover-up. Do this treatment ONLY ONCE. I made the mistake of doing it two nights in a row, and made my skin crusty because it was so dried out (I have dry skin to begin though)!
If you still have visible marks, or new pimples pop up!, you could wear a white camisole (lace?) under your dress. I think that it would look cute, to have a bit of lace peeking out through the keyhole, and no one would be the wiser!
Drink LOTS of water (including green or white tea, without sugar!) every day up until your wedding! AT LEAST 2L every day, up to 3L, even 4L, if you are exercising or spending a lot of time outdoors in this heat! It should help the spots clear and heal, as well as preventing new spots!

I used benzoyl peroxide (benzagel) just from the pharmacy section at the grocery store to get rid of mine. It’s what my dr suggested you could always check in with your dr/ dermatologist as well.

I was going to suggest applecider vinegar, but then i read the rest of your post haha!

Get some hemp lotion! I don't of drugs but I seriously swear by the benefits of hemp. I have a lotion that actually makes my tendonitis and carpal tunnel feel minimal, and I put it directly on any blemish and it's gone within hours!

Remember windex in my big fat greek wedding? That's how I feel about hemp lotions 😂

Order a Baiden mitten on amazon. I don't work for this company, I just want you to know that I do a lot of pin up styles and make up; before I found this awesome product, I was always dealing with bad skin and clogged pores. This mitten really takes off dead skin like no other!!! I have had it for 2 years now and still works like a charm. The only addition to my skin care is a homemade scrub comprised of 3/4 cup organic raw honey with 1/4 cup sea salt, stored in a glass jar. I use this once a week and all is good.

Get a gentle body scrub. You may be sweating more and the pores can get clogged. Gentle exfoliation will help your skin breathe.

Lately with all the last minute stress with me I've been getting pimples on my face. I read online that Vicks rub works so I decided to try and omg the next day it was gone. Seriously not a lie. Maybe try this and see it's worth a shot.

My FH swears by Spectro Gel's body wash. They have multiple kinds, including one for sensitive skin.