Should I go to the ER?

For about an hour and a half my right side abdomen has had a horrible pain it’s like a bad cramp? I’m not sure how to describe it I also really need to shit but every time I try to it just hurts to try? I’ve also missed my period by twenty days I don’t know if that’s relevant but I would have no clue if I’m pregnant as I got a blood test a week ago that came back negative plus I have irregular periods so I have no clue when is really supposed to be on it’s way. The only time it doesn’t hurt is when I sit up but when I lay down or touch around the area it hurts. Partner thinks it’s appendicitis but the only other symptom I’ve had of that is vomiting a little over the course of a few days but if I am pregnant that could just be morning sickness