What Causes White Patch On The Head Of Penis?

Hello sir,this is vamsi and iam from hyderabad.iam having a problem wit my pennis head.initially my pennis head is pink and one white colour patch is appeared.it is no pain n no harmfull it seems.but it looks ugly .i showed to dermotologist and he says nothing to worry. And another problem from last one year is my pennis foreskin tip got some white marks n getting cracks while having n after sex.ian not a Diabatic patient.pls mention some medicions for white patches n cracks. Crack pains r unbearable.kindly help me sir.