Everyone's skin is different and heals differently. I struggled for a few years with it but here is what has finally helped me.
First, I would cleanse with a gentle cleanser that your skin likes. For your body, you only need to cleanse once per day. Only wash off again if you've been sweating a lot. Also, make sure that the cleanser does not contain any alcohol. Alcohol will dry out your skin, stripping away your natural oils. When this happens, your skin will respond by producing more oil - which will cause more acne. So, be careful here.
Next, I would exfoliate with a gentle exfoliator - and do it REGULARLY. This depends on your skin type. Exfoliating your skin will help remove dead skin cells that get trapped because of too much sebum (oil) on your skin - causing pores to get clogged...thus forming acne. Most people think that by scrubbing their skin, they will get rid of their blemishes but you could be doing too much. Here's what I recommend: With oily skin, you should exfoliate 3-5 times per week. If you have dry or sensitive skin, only once per week; Normal skin would be everyday. Also, the skin on your face cold be different than the skin on your body. So, if your face is oily but your body isn't, make sure you exfoliate each body part based on the skin type.
Next, I would spray my problem areas with the following home made solution. Get a spray bottle and mix a water / vinegar solution. Apple cider vinegar is good but you can use regular vinegar as well. I use a 1:1 ratio but you can use less vinegar if you'd like (you may want to start off with 90% water, 10% vinegar to see how your skin reacts - work your way up, if needed). Then, spray the problem areas at night before you go to bed then shower in the morning. If you normally shower at night, go ahead and still spray it. The "vinegary" smell should dissipate but you may still want to wash off with a wash cloth in the morning. This can be very helpful for your back.
As far as the scars, these should fade over time. But, try the above to keep away the acne so that you don't get more scarring. The exfoliating will also help because it will help remove the dead skin cells that make the scarring look worse. Just be gentle with your skin when you exfoliate.
Controlling acne doesn't have to cost a lot of money. Just by making some minor changes to how you handle your skin and by being consistent with your skin care regimen, you should see dramatic improvements. Good luck to you! And, have fun at your Quincenera!!!