Period only for one day after having Sex

Patient: I am worried of my wife periods, I recently got married(2 months) and we do not want children for at least 2-3 years. But we had unprotected sex for 5-6 times till now and this month she had her period that last only for one day and that too a 2 days earlier, she said she usually have her periods on 24th, 25th of every month and lasts for 3-4 days, but this time she had on 18th only and it was only for one day.So my question is, Is there any chances of being pregnant and if yes what should be done to avoid pregnancy, also we don’t want children s of next 2 to 3 years, so what can be done to avoid pregnancy in future also for at least 2 years ? Please kindly help me