Glans always red?

Hello everyone, ever since I was with my ex-girlfriend I've unfortunately had a reddened glans with spots on it. I've already been to the doctor, but the swab test didn't find anything wrong. He prescribed me an ointment and since then it's been better. However, I still always have the feeling that my urethra is burning a little and that it itches every now and then. Unfortunately, my ex was often unprotected during sex and I had unprotected sex with her for the first time and every time after I had unprotected sex with her (2-3 times at most) I had this severe irritation. Do you think there's something serious behind it? I've always been careful and don't want to get any kind of disease… otherwise I'm really fine, it's my urethra that burns sometimes and my glans.