You had protected sex. That means you aren't at risk for any of these things you keep testing for. You have no reason to test again.
I understand that when she finished you with a hand job, some of her vaginal fluids may have been involved, but that's not a risk, either. I'm including some links at the end that will help explain that.
Please do not self-medicate. Taking antibiotics you don't need causes resistance to those.
You've driven 14 hours, spent 800+ euros, developed an anxiety disorder, and you had no risk. Make sure you are drinking plenty of water, lay off any alcohol and caffeine, skip the fruit juices acidic fruits like oranges (all of these can be irritating to the bladder and urethra), and give it a week. See how you're feeling.
Here are some posts from our experts (when we had them) that may help -
https://
www.medhelp.org/posts/STDs/Nervous-about-mutual-masturbation/show/2183476
https://
www.medhelp.org/posts/STDs/Mutual-Masturbation-STD/show/1968429
https://
www.medhelp.org/posts/STDs/mutual-masturbation-sti/show/1858544
https://
www.medhelp.org/posts/STDs/Understanding-the-risks-of-mutual-fingering/show/1516796
https://
www.medhelp.org/posts/HIV---Prevention/Vaginal-fluid-on-hand-touched-inside-of-condom-and-head-of-penis/show/1119533 - read this thread thoroughly. There is an excellent explanation about why certain activities are not risks, and why others are.
So first, when you have vaginal intercourse with someone, even with a condom, you will be exposed to her vaginal fluids. The condom doesn't protect all the skin.
I don't know who told you that at the lab, but they are wrong, and are just as alarmist as you're being. Most people who work at labs aren't doctors, either.
Hand jobs, even with an exchange of fluids, are just not a risk for anything. By the time she took the condom off, got you situated on the bed, etc., everything had pretty much died if she had anything.
Also, remember that sex workers wear condoms for their protection, not so much yours. Their jobs depend on not getting STDs. They are, by necessity, more concerned with not getting something from you, than they are worried about giving you something. This means most don't actually have an STD.
You weren't at risk for HIV (so your symptoms can not be HIV), any of the hepatitis viruses, (and depending on your age, you probably have been vaccinated for hep B), and your tests have proven that you don't have gonorrhea (the clap) or chlamydia.
Also, most people don't have HIV.
Semen leakage after ejaculation usually isn't cause for alarm. It can indicated an infection, or a problem with your prostate, but most of the time, it's normal. If you have a prostate problem, that could be affecting your erections and your semen. Your anxiety could be as well, but only an exam will determine this. If you do have a prostate problem, it's not related to this.
I think your anxiety is taking over. You are having nightmares and walking the streets, and not sleeping, etc. It's important that you talk to your doctor about this.
I suspect that your anxiety is not new. Have you heard of catastrophizing? https://www.theguardian.com/lifeandstyle/2017/dec/29/stop-catastrophising-expert-guide-psychologist
Talk to your doctor about your current symptoms, and your anxiety. You deserve relief from your anxiety. There are great therapies and medications available.