Wow, this is our 5th BFP! I am so excited for you! It's not an evap for sure, and very tin chance of a chemical, no more than anyone else, so 99% it is your own healthy baby growing!
CONGRATULATIONS, BUMP! You have now graduated to the I-am-gonna-now-google-even-more part of ttc !!have you shown DH yet?
https://i1270.photobucket.com/albums/jj605/katrus78/Baby%20and%20Bump/675735cc.jpg