Pregnancy questions please help!!!?

First of all..you are tooooo paranoid. Your level of paranoia could actually stress you into a miscarriage. None of the questions that you are asking are really important. You could know the answer to them all and still not change your situation. Once you have conceived, you leave it up to the body to do the rest. If your body will miscarry, there is nothing you can do to stop it. As far as your questions...all dates related to pregnancy are simply approximations (not precise). Stop worrying and go for a pedicure or something relaxing