18 yr old intrusive thourghts

Hi I would just like to ask for some advice my 18 yr son has been withdrawn from college last month due to his attendence and other issues he started getting these thoughts back in September 2018 he was struggling with college and college work due to his sleeping problems but since then his ocd has got worse he is having bath or shower  2 to 3 times a day constantly washing his hands tiding his room struggling so hard to watch meltdowns more too the doctor  has giving him Mirtazapine and doubled it to 30 hope this will help any advice would be grateful. Thank you .