From your history & clinical description it could be one of many things but a fixed drug eruption
, Hepes or a florid candidal infection feature foremost on my mind.
Do visit a deramtologist/venereologist nearest you for a better assessment on the ground.
For your history to be complete, you need to mention your sexual history in detail & both or all partners' have to be treated to prevent recurrences.
Also remember that in infections, the fomites: bedclothes, undergarments, towels et al have to be all treated: wahing in hot water & drying well in bright sunlight & /or ironing well with a hot iron should suffice.
I would go with oral medications & a Kit comprising 2Gm tinnidazole & 200mg fluconazole
will be ideal but may require a medical practitioners' prescription unless you have a very kind hearted pharmacist near you ;-)
Wish you great health & if sexually active, please practice 'Safe Sex'!
Dr Praveen Rodrigues MD
, Cosmetologist, Venereologist
Vikram Hospital, Bangalore, India