Welcome Gina. So glad you found us, and what a nightmare you have been having! And seems the school system has let your son down too. As I mentiond in a previous post, it is not just the discipline model, it is somehow the way we are trying to make all kids the same, so any that are different are labelled. Underlying causes for behaviour are also vital but so often get overlooked, as in your case.
The fact that your son has friends is terrific. Make sure he tries to keep in touch with them as it is so easy to loose contact. Are they aware of his problems?

Changing schools carries the problem from one venue to another in most cases so you are I think, wise to hesitate in trying yet a new school. What about another diagnosis now you are in the UK? And have you considered medication, which might just take the edge off things so that your son feels able to take those steps forward?
Ignore the schools complaints of how much school he is missing, this is purely based on schools wanting to or needing to tick the attendance boxes for students so that they don't get into trouble. Legally, they have to provide support, work and even tutors when a child is unable to attend school due to health issues, and your son clearly has health issues;mental health that is impacting on physical health.

Can you get a CAMHS assessment? Unfortunately, as if you haven't enough to deal with, you need to be as assertive as possible to ensure the school is giving the support they are required to give.
As you know, you can't force your son to go and if he is throwing up, vital that he be given some options.
Apart from the ideas above, would your son look at maybe attending for just maths and English or subjects where he gets along ok th teacher, or a couple of hours a day instead of full days, perhaps untill support is in place or any medication you might try takes effect. It might just keep the link open that is needed. He can tell his friends he has a sickness of some kind and has to take time out or spend less time at school until he is better. Sometimes the knowledge that they are not stuck there all day with no escape, can help.
If he is at school and feels he has to leave, is there someone at the school, or a friend or neighbour who he can go to? Just thinking if you are working, it makes it more fearful for him, as to where he can go or who he can go to if he feels really bad whilst at school. Some people organise that their child goes to the library and the librarian is worded up on this beforehand. Or some schools allow the student to sit in a quiet room near the office, where they can have a teacher or head just pop by to see if they are ok, Again... your son would need to make sure his friends understand why he does this, so feeling ill, is probably his best excuse, as that is, in fact, what he feels.

So if I was you I'd be asking the doctor about medication to help the severe anxiety that your son is suffering and then perhaps also asking the school what they will so for your son. It sounds like they need to understand that your son's 'behaviour' is a result of a lot of other things going on in his mind, and not intentional. And they need to understand the face of anxiety is often not a shy child, but can be a usually confident, friendly, highly intelligent child, who is crippled when the anxiety hits, or who might 'act out' in order to cover that build up of anxiety. Many teachers seem to think anxiety is only in the shy child. Interestingly, the 'shy' child does not necessarily suffer school refusal!

As parents we end up being the carers and the educators of others. Stress to the school thst this is a mental health issue and as your son is a teenager, their understanding is vital.

Let us know how you go. It is hard to even follow through with suggestions, I know, as we end up so mentally drained ourselves. But some of these things might just give your son the space he needs to take small steps forward. Believe in him and let him know he is feeling something that will be able to be managed and he will feel well again. And let him know he is not alone also.
Take some time out to do something just for yourself as well, and getting counselling yourself, can help your own strength.
You are doing all you can and a good mum. You will find a way forward.
Take care
Linda

Hi Gina

JUst wondering how things are going for you and your son?
Have you found a way forward or some help in some form?
Hoping your son is able to take those small steps forward, and remember that education does not have to be in a straight line,
All the best for chrisfmas and some relaxing times with your son.
Linda