Hi, I Took Postinor2 On 27th And 28th All At

Hi, I took postinor2 on 27th and 28th all at the same time. I had my last period on the 18th of march and I expected it to come on the 18th of April but it did not come though I bled for about 5days after 4 days of taking the pill pls wat does this mean? Am so scared I don't know what to think. I ran a test yesterday and it came out negative. Tanks