My friend involved herself in a sexual activity on 29th July. Her last second period was on 28th May and last period was on 4th July. Now she was expecting her period around 4th August but it didn't come. She then came across period like bleeding on 16th August and it continued for three days. Now she is confused if it was periods or implantation bleeding (she read about implantation bleeding online) She has taken home pregnancy tests twice. One on 12th August and other on 20th August. Both turned out negative. So, it was period or not? What are the chances that it was not period but pregnancy?