Either the pregnancy
confirmation test that you had way back was wrongly interpreted or the sonogram was erratic since it cannot happen that pregnancy cannot be visualized in a sonogram after so many weeks. It is true that cysts can cause absence of periods, but they do not lead to a positive pregnancy test and they are clearly visible in a trans-vaginal sonogram. The fact that you did not have proper withdrawal bleed also hints at associated hormonal
imbalance if pregnancy is not present. Weight changes, stress
, infections or trauma could add to the problem. Please get a complete evaluation before proceeding further. Hope this helps.