Bleeding early second trimester

Looking for any experiences or insights. I’m 16 weeks pregnant after IVF with PGS tested embryo. I started bleeding tonight and am hysterical. It’s bright red blood, enough to need a pad. I’m also having mild cramping. I’ve had lots of normal ultrasounds, last a few weeks ago. I have a call to my OB but am wonderful if anyone has experienced this or what it could be besides a loss? I am so heartbroken