From what I'm hearing you say, you're not sounding as shy as you are self-conscience and anxious. Having ADD is definitely a contributing factor in that. How can you feel confident in what you say when you've had numerous experiences with people degrading you and your intelligence. These are clearly people who are not understanding what ADD is all about.

As for not liking people seeing you cry and comfort you, well why would you? These are the exact people who've been so unsupportive and disrespectful towards you. I don't blame you. With comfort comes trust and you clearly don't have trust in the people who are trying to comfort you. This isn't a reflection of who you are - it's a reflection of who they are: ignorant.

In order to regain that self-confidence, you'll need to work through some of your internal scars first. This will take a lot of soul searching; a lot of patience; and a loving and supportive network. What you DON'T need is some doctor prescribing you some medication and treating you as another number.

Here's a theory of mine:
The reason why you write better than you speak is because the words you're using are right in front of you (on the screen). Are a visual learner? It's almost as iff all the letters floating in your mind are organizing themselves nicely on your screen and your focus releases the stress in find the words to begin with. When you speak, you have no visuals and the words are scrambled all over your mind.

If I were you, I would look into getting yourself into a support network for people with ADD specifically. That's a great starting point in making some new friends. Also, believe it or not, change your diet. I'm only assuming it needs a bit of tweaking. Lastly, find something that you're good at and build on that. I know it's a lot easier than said but it goes a long way.

I have ADD. I completely understand what you're going through.

Hang in there!
Huggs to you.