You describe it as red and irritated but no discharge. At this time keep it clean and dry. Do not use soap on the area. Apply antibiotic ointment such as neosporin, for a few days. The ointment will also keep it somewhat protected from the urine and the rubbing against your underwear. Wear cotton because it breathes well and doesn't retain moisture. Silk underwear may work well because they are smoothe. Either way, avoid the friction and apply the ointment. If it does not begin to heal then you will have to go back to the doctor for a urine culture and a swab of the area to determine if you have an infection.