Thanks for the query.
According to your description the possibilities are:
-Miscarriage: early pregnancy
loss with out detecting the positivity of pregnancy.
-Delayed periods: due to factors like stress
and strain or due to usage of emergency contraceptive
To rule out the possible cause you can go for beta HCG
If you don't want this, you can just track the ovulation in this month and can plan intercourse in that period, which will increase the possibility of pregnancy.