Need help please

I have just found out I am pregnant but there is a catch I went in to make sure and the doctor told me my hcg is low and need to be higher but I have had really bad cramping it comes and goes as it pleases and it hurts to the point I want to curl in a ball I am supposed to get AF tomorrow and I have not had any bleeding. I don't know if I should be worried. I have to call tomorrow and make a appt to get it rechecked. Need advice please