I would cal up the obgyn office and tell them what's going on and ask if you need to go in right away. Normally with patients that need to be seen right away they will make you a priority or tell you what's going on. But please see a doctor
Sounds like your uterine lining being shed as happens every period to varying degrees (sometimes noticeable, other times not). Most likely nothing to be concerned about, but you can talk to your gynecologist if it will comfort you.