Thanks for posting your query.
It seems like there is probably Balanophthitis or Epididymitis
is you. Please get an ultrasound
of the scrotum
as the testicles have become painful too now.
You may need a course of antibiotics like Azithromycin
and Doxycyline combination for 2 weeks or more. You need to take a complete course of the antibiotics.
You should stop using the latex condoms as the rash develops after using it.
Maintain a good personal hygiene with a mild soap. You may use calamine
lotion on the rash to soothen it. Do not apply any other medication on it.
I am glad that you are negative for the STD tests. Even I do not think it is herpes.
You should be fine soon.