So I'm 18 days late today. I've taken a HPT and I've had one taken at the health department. Both tests came back negative, but about 4 weeks ago I THINK I experienced "implantation bleeding." I'm unsure of what I should do now? I'm going back to the health department this coming Monday for birth control, but if I haven't started my period by then I'm having a blood test done. Anyone have any advise or anything??