Stress is the main culprit in the majority of cases of irregular periods
after excluding pregnancy
and this appears to be the same in your case. You may be experiencing some amount of hormonal
imbalance owing perhaps to stress; yet, since you have not responded to withdrawal effect of progesterone
, you would need a trans-vaginal sonogram and a complete hormonal profile as well as a general physical examination to see what has caused this. You may need a course of combination pills to set things right. Please maintain a healthy weight and a healthy diet. Hope this helps.