Okay, first, chancroid is an STD that is pretty uncommon. It's not syphilis - that's a chancre sore.
Your friend isn't qualified to diagnose you over Snap. What antibiotic did you take? Chancroid requires specific antibiotics in order to cure it.
This could have been a fungal infection, an infected hair follicle, eczema - the list is endless. How close to the genitals was it? It could have been herpes.
Nothing converts into HIV. HIV is it's own virus. It starts as HIV and stays HIV.
No. Syphilis does not convert into HIV and you've already asked and been answered about your risk of HIV on the HIV forum.