Hello, Thank you for asking your query at DoctorSpring.
From your symptoms of red lime on head of penis after sex indicates its due to friction.
Because of friction due to dryness there is chances that you have developed red lime on penis. But it would be better and a prophylaxis to do herpes simplex test. I also suggest you to use condom during sex and a lubricant, so that there would be lesser friction. I also suggest you to not rule out the possibilities of infection. Watch for any symptoms like fever, enlargement of lymph nodes in inguinal region. Also maintain hygiene by washing regularly.
Hope this helps. Please feel free to ask follow-up questions