'I nearly had my arm severed'
Callum has been in and out of hospital "countless times".
"I've nearly had my arm severed off. I've been stabbed in the head - fractured skulls, stabbed in the back, punctured lungs. It's amazing I'm still alive," he tells the Victoria Derbyshire programme.
But since January 2016 a scheme in Scotland has helped turn his life around.
Watch the BBC's Victoria Derbyshire programme on weekdays between 09:00 and 11:00 on BBC Two and the BBC News channel.