I had unprotected sex around 16 days ago, and took plan B within 48 hours of the first occurrence. 2 days after taking the plan B I started bleeding heavily like a period, but it did not last as long. I had unprotected sex again 2 days ago, but started having this dark brown discharge that I took as the start of my period. Now that I'm doing more research I am worried that it isn't my period but implantation bleeding. Please, please tell me that it isn't, and that I have nothing to worry about.