It is possible to diagnose the illness based on history. This would be asking you questions about the disease. Examples are: is it painful? does it itch. By asking questions like this, it is possible to narrow down the possibilities to nearly zero.
However, a test is needed to confirm the diagnosis. What you should do is to consult a MD medicine and ask him to do a tzank smear. After the tzanc smear, you will be able to tell if the person has herpes
Hope this helps.