Here, you need to undergo one blood test
for beta-hcg to rule out product of conception or miscarriage
. TVS scan gives some additional information.
Other reasons of irregular period are stress/ anxiety, hormonal
imbalance, pelvic infection
, over wt, irregular diet pattern, uterine pathology etc.
Consult with your gynecologist for proper examination & relevant investigations. Take suggestive measures accordingly.
Practice safe sex in future. Good luck.