miss two periods now cramping really bad

Jane
I haven't had a period since 3 rd November I've missed two periods in a row I had a negative hpt yesterday. I'm booked in for bloods on Tuesday as the doctor was worried I could have a blighted ovum.
I have started experiencing really bad cramps different from af cramps also shooting pains. No spotting or bleeding. 
It's so painful I can hardly walk any idea wat it could be?