What Causes Recurring Rash On The Penis After Sexual Encounter?

iN 2011 i came in sexual contact with my girl friend. after few days i saw some rash on the front portion of my pennis. I met with a doctor and after taking some medicine it was cured within 3 months. 15 days ago I came in sexual contact with that girl friend again. And saw the same symptoms again. this time rash in the mouth has also found. I am in tension. What should do now ?