Concern for missing periods. Go run?

My girlfriend had an I-pill on the first week of March, and because of that she might have early periods that month. She is saying that she missed her periods schedule in the later part of March due to that. The only thing that is running through our minds is that we had unprotected sex on 19th March and that could be another possible reason for missing the periods this time. Her recent symptoms show no signs of pregnancy. Few days back she had a lot of white discharge but since then she's completely fine. what could be the possible reasons for missing the periods then? She claims that it was scheduled to happen in the last week of March, and it's been almost 2 weeks that has passed. Kindly help. Any medications that she needs to take our any tests that we should go run?