It sounds to me like you could have a learning disability but it is true that it can take a very long time to get help. I suggest you go back to the disability officer and say you want to get assessed by an educational psychologist. If you do have a disability, he or she will be able to identify it and then you're entitled to help. This isn't likely to be an easy process and it's true that some schools try to ignore disabilities because they require extra effort. Don't allow that to happen - you have a right to help. If it takes time then rather than stressing yourself out maybe you should take time out before trying to do your A levels - wait until you have the help you need and then give it a go. I admire your determination, but sometimes you have to give yourself a break.
On another note, you have to think about the long term. If you do go to university, will you be able for it? Will you have the same problems again? Not going to university does not mean that you'll necessarily end up in a dead end job, there are other options out there that might suit you better than the academic life that can lead to well-paid fulfilling careers. Like I say you seem like a determined person, and that's all you need to do well in a career that really suits you - a university degree isn't necessarily the be all and end all.
Good Luck