With Polycystic Ovary Syndrome, periods can be irregular, and medicines like Deviry are often given to induce a withdrawal bleed, which usually occurs after completing the full course and stopping the tablets, sometimes taking up to 7-10 days to start. Since you had unprotected intercourse 3 weeks ago, a negative home pregnancy test is reassuring, but for complete certainty, you can repeat the test after a few days or get a blood test (beta-hCG). For now, continue the medication exactly as prescribed and wait for a week after finishing the course; if you still do not get your period, or if you develop symptoms like severe pain or heavy bleeding, you should revisit your gynaecologist for further evaluation (such as an ultrasound or hormone tests). Avoid taking additional medicines on your own, and try to maintain a healthy lifestyle, as PCOD-related irregularity is common but manageable with proper care.