Heavy period

Bonnie
Has anyone had a very heavy flow with large clotting? I usually have some clots but not very big, but now I'm having nausea, and bled through a regular tampon in like 20 minutes! I'm nervous about endometriosis or something else serious. I've been ttc for 17 months now. I'm seeing my ob next week and will ask but scared I should maybe go sooner? Please help!