Bleeding Queation

Jody
Ok.....I am new to this site and have a question? Guidance would be greatly appreciated. So my fiancé and I have been TTC for roughly a couple months. I was not set to get my period until the 21st of this month and all of a sudden today I started bleeding out of nowhere! It started off very pink and now has turned over to darkish brown. My cycle is very predictable and comes at the same time every month. Can someone help me with why I would have started this bleeding 6 days before my expected period?