It is a mystery...my general experience is that my own Acne is caused by candida. Was your diet any different at the friend's home? Less carbs and sweets, which encourage candida? Maybe the water is different?
Since you've been to so many doctors, I would suggest an incredible computer that diagnoses (and treats) illnesses. It is explained (with local practitioners mentioned) at quantumsource4life.com and is reasonably priced, given all it can do. I use it with my dr and have never been so impressed; it is the medical tool of the future. What have you got to lose? Read my past posts for more on it.
Another thought...testosterone can make Acne worse; do you work out at the friend's home? Working out can increase testo, so have you noticed any diff when you DON'T work out? Good luck.