So I asked 2 weeks ago about the changes of being pregnant, my story was that I have this fertility calendar and it tells me when I'm ovulating and going to have my period and it is always right, I start exactly when it says, I had a period end Feb 26, and it said I should have ovulated March 6th and that my next period would start on the 20th. On the 15th I had sex, we used the pull out method and I understand that's bad, cuz of pre cum and all that but he also went pee and all that before so it kills off any sperm in precum right? Anyways I then had my next period come on time on the 20th and it lasted 6 days, perfectly normal heavy period, on my calendar it says I have about 9 days till I start but this morning I went to the bathroom and there was dark blood in my underwear, I sat there and wiped and everytime I wiped it was there so I put on a pad this morning just to see if it's a lot, I'm freaking out, can this be like implantation bleeding?? How is that possible if I had my period? I need some expert advice