Help?

My period is 19 days late, I've taken 4 pregnancy tests which were all negative.. my stomach is extremely hard to the touch from about my belly button down to my pelvic area. I've been having terrible cramps and they seem to be staying towards the right lower side of my stomach. Sometimes they are so bad they bring me to tears. I feel as if I'm being stabbed. I have no idea what's going on. I don't want to go to the ER and the doctor is booked for the next few days. Any ideas what's going on?!