HCG levels low

Yesterday I went to the ER for terrible back pain and cramps due to constipation is why I went. after doing series of blood work as well as an ultrasound I was told that my levels were low and that either I am earlier than what my cycle has led me to believe or that my pregnancy is resulting in a miscarriage which I am not trying to believe! I just hope everything changes tomorrow when I go back for my updated blood work has anyone else been through this please answer!!!