If I get pmma butt injections, how long do I have until it goes bad, and why do some girls have complications and others don't?

That is a very good question. Those filler are substances that reacts very badly in the body in short or in long term. You never know when problems will appear, some times years pass till the problems begin.That is why Plastic Surgery do not approve these fillers. When reactions begin and problems appear there is no way to deal with them. The more you try, the more adverse reaction of this substances.Please stop getting this injections and look in the internet on Google for "Butt Injections Go  Wrong" an you will see a lot of terrible cases.When this patients come for help is very sad to tell them there is nothing to improve their condition.

Hello. I am concerned that you are trading safety for your quick result. There are real issues with non-certified or under-certified practitioners injecting all sorts of substances into the buttocks.  I understand your desire for curves, but think SAFETY first.  Good Luck.