Hi Redsky Sorry to hear your ds is finding things difficult right now...
You mention that he loves his activities, he enjoys working, he has been prone to anxiety... etc... it seems to me that he is a hard working, hard playing young man going through a tasking time of his young life. I cannot see much that isn't "normal" here.
If you don't mind me saying - you mentioned that you have had difficulties yourself in the past and perhaps your stress for your son is having more of an effect on him than you realise. This is bound to have a nerving effect on you... he is your son and we all want our children to do well.
Are you perhaps unwittingly putting the pressure on by taking on this worry? How have you reacted to your son confiding in you? Do you mind me asking - are you a single parent? Is there a "duty" your ds may have taken on himself to do better for you/himself?
There can be so many factors resulting in stress but the main one is success at this time for any 17yo who gives a damn about his/her future.
Stress of such types can have many outcomes, and a main one is lack of appetite - wieght loss etc.. keep an eye on this if you think he is losing too much too quick.
Try to get him to eat something but don't panic him into doing so if he really doesn't feel like it. This will only cause him something extra to worry about. He will eat when he is hungry. Explain the reasons why he needs to eat in a calm "mumsy" fashion - he may see sense and think again about it.
Have you tried herbal remedies such as Kalms, or camomile teas etc... ? The doc may have some idea of other remedies but try to stay clear of the Barbs ok?
This will soon be over and the next thing will be A2s and they will be a doddle after this... please try not to worry for your son... be there and support him, encourage and soothe. Be a friend but most of all be his mum.
Huge hugs and best of luck to your ds. I am sure he will do just fine.