You tested negative for all pertinent tests. Risk for HIV was zero, by the way. You possibly do have balanitis and can speak to your doctor about it but that is not an STD. So, give up on the std thinking and look for other reasons.
Hi
1) the test should be conclusive
2) there are other stds that u can catch, such as nsu, parasites... Mycoplasma, etc...
3) perhaps you are suffering from blanitis