well there are many causes for the symptoms that you are having.With the irregular periods
i would first like to rule out reasons like PCOS,ovrian cyst,anemia,poor diet etc.Stress is a major factor in causing hormonal
imbalance and irregular periods.I would ask you to to have your hormones checked like thyroid,prolactin
,blood sugar etc as these may cause the symptoms you have.If your doctor has said that there is no pathology from the ultrasound
then i'm assuming that true.If you havent had any blood tests i'd advise you to have them done.Only then can we put this down to stress.