A twitching or pulsing feeling around the urethra is usually a minor muscle spasm in the pelvic floor, not a sign of anything serious, especially since you have no burning, no pain and regular periods. Dehydration, caffeine or holding a full bladder too long can trigger this kind of twitch.
Next Steps
Get a urine routine test done to rule out mild irritation or infection, since that can sometimes feel like pulsing too. Drink plenty of water through the day and cut back on caffeine and spicy food for a few days to see if it settles.
Health Tips
See a gynaecologist if it comes along with burning, pain while passing urine, or doesn't settle within a week, so it can be examined properly.