My girlfriend period is not coming.

Hello my girlfriend and I was involved in unprotected intercourse on 28june. We were not sure that the sperm goes inside or not. But she took ipill on the same day. There was no bleeding on that or following days. On 4 Feb her period comes as usual every month. But In March her period didn't come til now. We had done 4 urine test on 6march, 8 March,19&21 March all comes negative. She also had beta hcg test on 9th March. It was also negative. From last few days she is having some spot bleeding with brown discharge only few drops in the whole day. She is very tensed due to this. Also in March she had a lot of stress due to personal reasons. We have diagnosed with practo doctors. They told us that it's nothing to worry and suggest a pill to force period. What should we do now. Please suggest her period is not coming.