Your description does not resemble that of herpes
, but we can never be sure without a physical examination.
For whatever reason your doctor suspected herpes; the test has reported a negative result.
Another fact we cannot overlook is that you have not mentioned sexual contact but immersing yourself in poorly conditioned water, which could most probably have caused a bacterial infection and not a viral one. Another important fact is that you experienced a response to antibacterials therapy, which makes it even more likely for you to be suffering from a bacterial infection, not a viral one. A herpes lesion would not disappear with antibiotic therapy.
Please visit another doctor and get accurately diagnosed.