Delayed Period. Negative Urine Blood Test. Taken Duphaston. Have PCOS. Pregnant?

hello my girlfriend is 23 days late on her period, we had countless neg urine blood test her LMP was 24/10/13. we had B HCG Serum done last 6/12/13 with negative result. our ob assured us she was not preganant she started her on duphaston for 5 days, now 7 days off from duphaston but still no period. She was diagnosed PCOS a year ago, provera was given and she menstruated. PMS symptoms are still present now could she be pregnant or just a missed period....thank u so much!!!