I started my period last month on August 3, on August 20 I had unprotected sex for about 10 seconds and he did not come in me or was there much precum. My period was due on August 31, on September 6 I took 2 pregnancy tests that came up negative. On September 8 I noticed I began my period. It's going normal so far, but I want to make sure if it is implantation bleeding or not? I heard this is too late and that I am not pregnant but would like some opinions please! Thanks.