Help!

Hi all. Please bear with me, I am new here. 
my son now aged 21 was diagnosed aged 14 with high functioning ASD. We never had any behavioural issues and he attended main stream school. His issue has always been social and communication. He transitioned from primary to high school well but started to struggle which was why we decided to go for a diagnosis. Fast forward to college he did 4 A levels studied hard but struggled in the exams. Results were ok but not what he wanted. He has done some other online course and also his SIA security badge course but no one will hire him. He is now 21, not working, doesn’t go out, no local friends and has really isolated himself from us and others around him. He refuses to communicate with me, will not discuss his feelings and thoughts. I don’t push it, just make sure he knows I’m here to help. I work full time and am home based 3 days a week and office 2 days. He has recently been seen by the GP after some nudging for staff he completed the Kings Trust with. This was not helpful. He was advised to self refer and they didn’t want to see him again. He has self referred for therapy and we are awaiting an appointment. He does ok in social situations but will shut down once in his safe space. I’m so worried about him. He sleeps all the time. Is hardly active so has gained weight and his moods are terrible. He’s a big young man and I’m slightly intimidated by him. I am at a lose on how to help him. 
can anyone offer any guidance. I’d be grateful for anything. Thank you.