Ok, this might be a silly question, but I think I am losing some brainmatter and I can't for the love of me figure this out

You get your period, then after 14 days you ovulate. Ok, now you have sex and you are lucky that a sperm gets into the egg's nickers. Now is that conception???
Then comes Implantation, right. How long after conception does implantation occures? Then if you HAVE implantation, you can only test pg after 14 days with HPT, right?? But then they calculate your due date from the day of your last period. So you are infact always two weeks "before" your time, kwim??

Sorry, I am totally not getting english today and have been reading to much and now I am like a cameleon on a light show!! DUMB-STRUCK!!