Just caught up with this, harmen. Sorry you are going through this - it is upsetting isn't it?
My DS1 has some similar problems (barely legible handwriting, real difficulties recording anything on paper, although has it all in his head, poor concentration, problems with organisation, problems socialising etc), and for years school did little about it because they put lots down to our home situations. It has only been in the last year that things have really got moving after I told the SENCO I would get my gp to refer him if the school wouldn't.
He has been on school action plus for a few years, but wasn't really receiving that much extra help.
He has now started the assessment process, and I feel he will probably get a dx of dyspraxia, although he also has real self esteem problems, which makes me feel awful as a parent.
Don't blame yourself, harmen. It sounds to me like you are doing a very good job, and it isn't easy when your on your own is it?
Hope all goes well for you & that your DS soon receives the help & support he needs.