Talk to Gynecologist on Pregnancy Risk

My period date was 7 march but it still doesn't start. We had unprotected intercourse for the first few seconds and then protected till ejaculation at 5 March. Is it a sign of pregnancy or something else? I don't want to get pregnant. How to check it? How to avoid pregnancy if it's a sign of pregnancy? I did urine strip test yesterday (after 5 days of intercourse). it is showing negative. is it enough or should we go for another test? The delay of the period is worrying us. Note: No history of delaying periods.