My 20 year old sons ongoing headache

Help. my 20 year old son is constantly complaining of a headache, which when he  describes  the symptoms he appears to be a classic stress headache.  Despite taking him to A & E and the doctors on several occasions where no red flags were noted he is convinced he has something worse such as a thunderclap headache.  He has stopped going to college, seeing his friends, going to clubs and even moved out and staying with my parents as he fancies a change of scenery. He spends time just laying on his bed or floor stirring at the ceiling.  I do however manage to get him out once a day even it that's just for a coffee. He is too scarred to think because he is too scarred his brain will bleed.  Yesterday whilst in the cafe he started to ask me if his hot chocolate was boiling and he thought he had scalded himself and can not feel the pain.  I convinced him that was not the case and told him the drink was just warm and he calmed down.  The doctors told him to take ibuprofen for a week but then he got destressed that he could not feel the pain anymore so he did not know when to rest his brain as if he was using the headache as a marker to when to stop.

The doctor has referred him to neurology and also back to adult autism and adhd mental health. But i am stuck to know how to deal with this situation.  I am so worried so please any advise would be great.