If the hysterosonogram's results were fine, do I need endometrial biopsy also?

Depends. The workup of irregular bleeding has been changing and there is a tendency to move away from an endometrial biopsy but this is not the standard of care yet. Each test you have done that says things are normal is good news and shifts the odd in your favor that things are fine. An endo biopsy will give more credence that things are fine. Discuss with your doctor how far to work things up.
Hysterosalpingogram. A hysterosalpingogram just tells a doctor the shape of the uterine cavity an whether or not the tubes are open. An endometrial biopsy or Progesterone level helps define the condition of the uterine lining.