Is it implantation bleeding?

Okay so i don't actually know what implantation bleeding is but basically heres my story! I've been having sex quite a lot maybe 4 times a day on Friday through to Sunday, on Monday morning I've had the lightest spot of blood ever now and again about twice it's happened now, I get cramp and my nipples are killing! and I haven't done a test yet, is it implantation bleeding? Is it worth doing a test? My boyfriend already has a little girl and she was conceived within the first week they were together, is there such thing as super sperm lol! Please help I'm freaking out!