What Causes A Red Mark On The Penis Head With White In The Middle?

Hi i have a red mark on penis head with white in the middle, it dosnt hurts, or anything, my gf feels unconftable sometimes when we have sex, i dont know if its something i should worry about ive been trying to go to a doctor but because of my job i cant go on mornings and seems like most doctors only attend at mornings, can someone help?