Hi, I am actually under similar situation as you, despite my case is not as terrible as you(such as blood in semen), I guess.
I totally understand how you feel when all the test results show no abnormalities yet the symptoms keep coming back.
I also desperately went searching for all relevant things(expert opinion, research articles,etc.) Sometimes the more search I did, the more anxiety it brought.
So here are some facts and advices from me.
1.All the symptoms happening(ed) to you, except those on genital area, are unrelated to any kind of Stds.(since you have conducted so many times of blood/urinary tests, do not doubt their accuracy)
2. Those symptoms on genital area happened to you may not be caused by any kinds of illness.According to my doctor, recurring balanitis are quite common among healthy men. I also experienced recurring balanitis, my doctor eventually gave me creams that help keep my skin moisture. The creams work effectively, the rate of recurrence reduced greatly.
In my opinion, go see the urological doctor when symptoms appear. Ask them to do virus and bacteria culture/PCR.If nothing detected, that's it, as you have really tried everything you can. Beyond this ,it is merely metal problem, try to adjust yourself.
No more mastubation( forgive me if I guess wrongly). It really cause damages to your urinary system, even if you are not infected with anything. Your symptoms are also common among people with mastubation-addiction.(cold body, urinating difficulty)
Start doing exercise and other necessary things needed to enhance your immunity system. I also suggest you to discuss your problem with your partner(if any), I did so and it really made me relief, my girlfriend check my pennis (do not get it wrong) everyday,once symptoms are detected we go hospital together.Remember,all the illness that could potentially "ruin" your life have been excluded,(Hiv,syphilis,Hv),the worst thing that could happen to you is urinary problem, which is not a shameful thing at all.
Hope my comment is helpful.