Hi there. I'm sorry you are anxious as that makes like harder. First, let me say that it would be best to work on your anxiety with the long term in mind. A therapist would be excellent to help you learn to cope better with the worries and anxiety. Since you have ad/hd--- anxiety is very common to have with that. It would be beneficial to you to understand that you will always need to be aware of things with these two conditions that often overlap. Knowing what helps and what doesn't. Do you take medication for your ADHD? I know that physical activity also significantly reduces symptoms-- swimming, running, lifting light weights, a Zumba class, a kick boxing class, etc. All of these things are good in general for anxiety but often part of the treatment recommended for ADHD to make symptoms much better. So, make sure you are getting a lot of that in. Watch your diet as well as that can have an effect. Blood sugar can significantly impact things.
So, work on that as the root of the problem---- techniques for controlling your anxiety and ADHD. Your parents may allow you to see a therapist which would be excellent OR you can talk to your school counselor who may have helpful resources.
Now, you most likely do not have an std from giving oral. You tested and tests were negative. You have to believe it is JUST yoru anxiety talking. And if sexual activity causes stress, it should not be something you engage in at this time. NOT worth it.
Work on the anxiety though and you'll stop worrying about things you tested negative for. good luck