I think I would advise you to go and have this little lesion swab tested, please. It’s hard to tell too much from photos but there is something different there than the surrounding skin. Is there someone you can see today? The sooner you are seen the more accurate the test results.
As for the medicine interfering with an accurate diagnosis by antibody test. I don’t really know how your medicine would interact with your immune response to herpes. Can you tell me more about the medicine?