My hcg blood levels 120 and i gave lower back pains and light cramping . why could this be?

3 possibilities: This could be a normal early pregnancy, the start of a miscarriage, or even a tubal pregnancy. You will need your HCG repeated and an ultrasound sometime in the future. Keep you doctor advised if the pain gets worse or if you start bleeding.

Can't tell: A single HCG level without any other information like imaging cannot give a diagnosis, , could be signs of a miscarriage or an ectopic pregnancy or just an early normal pregnancy. Talk to your doctor and be sure to follow up as directed.