Well, we don't give any sort of HIV advice here as you were already informed about that.
That you have been informed that HIV is not a concern and you've completely over tested to keep making that point to yourself, you are left dealing with common health anxiety. You may not want to take medication for anxiety but that is not the only way to treat it (although it is something some need to do).
But talking to a therapist would then be the best answer. They can work through this irrational fear you are having so that you don't keep ruminating and testing and asking and wondering and worrying!
Everyone has worries and fears. Anxiety to some extent. But when it starts impacting us in such a way that feel we aren't really able to live the life we want? Then it is time to dig deeper for help with it. That sounds to be where you are at.
The ways to find a therapist are numerous at this time. You may know someone that sees a therapist that they can recommend. You can google 'therapist/psychologist that specializes in anxiety near me" and get a list of names. You can contact your health insurance (f you are in the US) or health agency wherever you are to find a list of options. You can now do therapy online with things like Betterhelp that you pay with cash but licensed therapists operate it for telehealth therapy. You can get a referral from your regular doctor. All sorts of options of finding someone to do psychotherapy with.
Then you can work on strategies to cope with anxiety and hopefully overcome it. That's what I'd do if I were you. If you find that STILL is not enough, maybe the subject of medication will come up but perhaps not.
So, take it one step at a time. Strategies of distraction can help, deep breathing, getting regular physical activity, solid sleep and good nutrition are helpful. Keep all of that in mind too but get someone to talk to about this and see if you can move past it. (you don't need to keep asking ANYONE about HIV anymore. You are on the right track to reach out about anxiety. )
Don't worry about meds. You don't need them. You sound like you'll never need them. They're for serious problems, and as you say, you're fine most of the time. Basically when you have one thing that gets to you even when you've eliminated the concern you have a phobia. Almost everyone has a phobia or two, so it's no big deal really. It's only a big deal when it gets in the way of your life. Given you're having a minor problem, what you're doing, if the relief lasts and keeps getting less, will actually lead to being a cure as eventually your brain will learn not to be afraid of this anymore. But a therapist who specializes in the treatment of anxiety might speed it along if it's a good therapist and you click with her. I think you're handling this well, as you've found things that ease your mind. If you ease it long enough, again, the anxiety will go away. Meds are never a cure, but stopping thinking about it is. How you get there is up to you, but again, don't worry about meds, you're in no way near having a bad enough time to add that to you worries. You do want to get over this, though, because sex is fun and you don't want to make it not fun. And when you do successfully put it behind you, you'll be that much stronger. Peace.