You say you work in an office: i.) I wonder if you drink lots of coffee throughout the day? If you do, try and vary the types of liquids you drink during the day! ii.) Offices are often WONDERFUL social environments to start building real and appropriate relationships with the kinds of people you are attracted to. I would suggest it is better to think of people you are not directly working with, may be in another office, you may regularly meet certain people going to work, at lunch times, in local shops. I think you may find it more satisfying than risky sexual relationships with strangers.
I think you are realising the real issues with sex with strangers - YOU need to draw YOUR own conclusions on this and act accordingly in future. This is why it is best to build up a relationship - get to know people before you start having sex with them is the safest, and more rewarding approach!
When washing your penis, cool to warm water NEVER HOT! If you cannot wash, go in a toilet cubicle and use the toilet paper to make sure you are 100% dry. Then when you can, wash properly with warm water.
Think when you are in a shower, if you like a really hot shower, to protect the skin at the end of your penis (and, protect from soap / shower gel / hair shampoo etc that I have already mentioned).
At home / where you are staying, you should have a towel that YOU ONLY use to dry your penis. Change the towel regularly, and wash it in non-biological washing powder, or if you do your own washing machine wash, try getting liquid soap flakes to ENSURE you do the towels, also do your underpants / briefs / undershorts at the same time.
When you go to get your test results mention the burning sensation as you may have a urinary tract infection - you certainly still have something causing a considerable irritation to your penis!
As you say yourself: “I miss the days when I was healthy” - you need to learn from the process you have been through due to the casual sex, put this in your past - become fully health again, and I would suggest the best way to avoid STD / STI conditions is learn how to develop more satisfying, longer-term relationships with people you can trust!
Good Luck ……