Hello Sir , I Would Like To Ask You One

Hello Sir , I would like to ask you one doubt which i had from many days , sir please can you tell me , when i roll back my penis foreskin from head top of penis foreskin ,it has very very very tiny blisters at top of the skin, its only visible in flash lights not painful either,which can be seen by flash lights only , when it completely roll back , its on skin , is it STI or just common infection due to friction from underwear ??, i had sex only once with condom , and i just have multiple blowjob , 4 month ago

Thanks