While different countries, I am pretty sure things are similar if not the same.

I mentioned earlier forms of proof documentation. Yes, retrieving a birth certificate can be a lengthy and expensive chore - but a baptismal certificate is not. Simply visit the parson of the parish you were baptised at (I assume you were as it is commonly expected it be done so over there). They will have a record of the sacrament and will generally re issue a certificate at no or little charge.

Surely you have a government issued health card there. Student ID with a picture? Social Insurance Card? All these are also recognised source documents.

If these are difficult tasks, find yourself an advocate to assist you. As another person suggested, your local mental health organisation should be able to provide you one. If you are in school. a guidance counsellor will help. You do not have to bear the brunt of this alone.