There are several reason of irregular period. You had one miscarriage
and negative test for STD.
Possibilities are hormonal
imbalance or ovarian pathology (PCOD) or may be from stress, emotional upset, thyroid
prob, over wt/extreme loss etc.
Do a USG for lower abdomen and some hormone tests.Then consult with your gynecologist and take advice accordingly. Also need some gynecological examination.
Take healthy diet (LOW carbohydrate
), avoid stress and do regular exercise or yoga.
Be well and take care.