Thanks for the query.
Combined oral contraceptive pills
Fe 1/20 can cause menstrual irregularities as side effects.
And your delayed periods may be because of that. Though you didn't have any problem in the past hormonal imbalance can develop at anytime as many factors can influence that.
As you used the pills according to guidelines the chance of pregnancy
is very less.
Anyhow if you want to rule out the pregnancy better to go for blood test
for pregnancy once as it can give accurate result even in early gestation.