Hello painless and non itchy white gray spot for 15 to 20 days can be caused by a sexually transmitted infection like Chancroid, syphilis or other infections You need to be worried but not too much until diagnosis confirmed In my opinion you must book an appointment with your doctor or an veneral disease specialist for physical examination and further investigations If you can upload a photograph I will be able to help you better You should maintain good hygiene Use.condom while having sex, there are possible chances of its spread to your partner You should clean it with antiseptic soap or solutions and apply an antibiotic ointment Hope this answers your question Please feel free to ask for more assistance, I will be happy to help you Best wishes