uR, I'm really sorry to hear that your son is getting ready to have more tests. I'm sure he gets tired of tests and the pain. There are some really good home remedies out on the net for cystic acne. You may want to do a search and have your son try some of them.
Your son will find his footing and he is amazing right now. He's really an inspiration to everyone and don't think people aren't aware of what he's going through. Maybe he should write a book about his life and life experiences. You'd be surprised at how many people would read it. Writing about one's life experiences, especially when there are major health issues, are very popular with people today. Why? Because people want to learn about health issues and how people are dealing w/it.
Just some of my thoughts today. Tell your son he is simply amazing!
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.