First off please know that you are not stupid and you are not lazy. Secondly, the fact that you recognize you might need help is a sign that you are aware of what is going on. I would not be afraid to talk to the school psychologist. If you tell them that you feel out of control and explain it like you did in your post (maybe even print out the post and show it to them for clarity) they will probably talk to you about how long this has been going on and will try to figure out the cause of your problem.
There could be many reasons you are having trouble in school; it could be ADD or it could be some other underlying learning issue that hasn’t been diagnosed. It could be a number of things.
Lastly, I recommend you also talk to your parents. Sometimes parents say things w/out realizing the impact, or they say things without intending to label someone. When you say they are stigmatizing ADD, they may not even realize they are doing so. And I’m sure their main concern will be your well being and if you tell them you’re feeling out of control and struggling with your school work they will be more concerned about helping you. It’s possible they won’t be able to understand your belief that you have ADD, so it could help if you printed out the articles you saw that talk about ADD to show them; give them something to help them understand why you think you have it.
Best of luck!