Horrible cramping

PLEASE respond . I am having probably the worst cramps. I was about 3 days late , I'm normally on time or early. I have endometriosis , I've had it for 4 years . I had sex last night, and didn't use any protection. Today, I woke up with a little blood and horrible cramping. Now it's about regular flow. ( which isn't common, I'm normally very heavy.) but these cramps are HORRIBLE. I'm wanting to go to the ER it's so bad. Is this implantation ? Miscarriage ? Cyst? Help.