Why do I have these cystic blemishes In my genital area?

Patient: I’m a 16 year old male and about 9 to 10 months ago, I used an electric trimmer for shaving my genital area. A few days after that, a bad cyst like blemish appeared and caused pain. It was very bad for a few weeks. It went away, leaving a reddish purplish mark. Its never been as bad as then but it comes and goes. I recently went to the doctor and all I was given was a sulfur based antibiotic prescription which didn’t do anything. I’ve been washing everyday but it hasn’t gone away. It gets worse more than better. I know my diet could be a problem to it but it all started when I shaved. The only thing I think it could be is an ingrown hair that is infected. It’s not on my genitals but the area right above. Please tell me, if you can, the cause of this, and how to make it go away. Thank you!

Symptoms: Pain, redness