Dear bhavin, if you had sex with any new or unknown partner unprotected then think of STD
APART FROM STD there are lot of organism affect penile top in your words, unhygienic condition of foreskin invites many micro organisms. only antibiotics generally don't help . generally its a mixed type of infection and takes longer time to get eradicated better consult a dermatologist
or a good physician, don't worry if you didn't had out side sex. If you are married get checked your wife also.