First of all, do a blood test
for beta hcg to confirm or exclude pregnancy
If you get negative result again,then possible reasons of irregular period like hormonal imbalance, stress/ anxiety,ovarian cyst
, thyroid problem,wt gain/extreme loss,irregular eating habits etc. are needed to be ruled out properly.
Here you need some investigation to rule out underlying pathology by USG pelvis,Thyroid profile, LH/ FSH, Blood estrogen & progesterone
level etc. So consult with your doctor and take suggestive measures.
To conceive in high percentage, your period would be always regular so that ovulation occurs in correct time.
Avoid stress, take healthy diet with iron & folic acid
supplements, control body wt and need proper sleep.
If you need further consultation with me,then you can visit http://www.healthcaremagic.com/doctors/dr-soumen-patra/63326.