Urethral opening redness and some discomfort. what could this mean?

Sounds like a UTI: Hydrate aggressively, avoid sugary foods, try cranberry supplements, avoid sex for a little while, wear cotton panties, but most of all, get a urinalysis including a GC/CT test. Antibiotics will successfully treat the infection. You can also buy pyridium (phenazopyridine) to numb the area - just be prepared for your urine to turn orange. Make sure you & your sex partner wash genitalia frequently with soap & water.

Urethritis: a urinalysis and check for chlamydia/gc should be done to investigate it, but it could be because you are fortunate to have an active sex life. The wives would get this after their husbands were gone for a deployment when I was in the service. Perhaps be grateful for what you can complain about.