Heavy Period Feeling

Hi mommas- I had a question about something I haven't experienced before. I'm almost 34 weeks along and for the last week on and off I've been having a heavy feeling in my lower stomach/ upper groom area- best I can describe it- that heavy feeling like right before you start your period. No blood. No actual cramps. Doctors appointment tomorrow morning. This morning it just won't let up- has anyone else experienced this and does anyone know why? Don't remember this with my first....
Thanks :)