If it's happening only one day of the month it could very well be cervical mucus.
I recommend you get an ovulation kit. Not all women ovulate in the middle of their cycles. The only way to know for sure is to use this kit. It's true that some women do know when they ovulate because they get the cervical mucus, but not all women get it. Some women will also have cramping for a day when they ovulate.
If you're TTC get a kit and track your fertile days for a couple of months. They should be on the same day.