you can't really know for sure unfortunately. its easiest to "guestimate" when you're fertile then to actually know for sure, as every woman is different. are you sure it wasn't ejactulation or your natural lubrication? i would say by the sound of it, it is
possible you are starting your fertile days or ovulation.
1. when was your last period?
2. how long is your average cycle?
3. are you just getting off birth control?
it is easy to find other informative articles online of how to track your cm. if you give us a little more information, we may be able to be of more help to you.
but, welcome to the board and we hope your stay is short and sweet!