My very own plot hole

My favorite TV show ever is Friends.  I love it so much and know it so well, that I could probably have conversations in only Friends quotes if I really tried.  So naturally, I've been reading lately about all the plot holes in the series, and also finding some of my own.  Well, today, I realized I have my very own plot hole in the story of my life.  

My birthday is August 1.  (Funny side story, a lot of my August rent checks were dated 8/1/79.  Back when people wrote checks.  But back to my plot hole).  My mom told me I was born 4 days after I was due.  She also told me I was due July 27.  One day, I realized that 4 days after July 27 is actually July 31, not August 1!  This leaves me with so many questions!

1. If I was in fact 4 days late, was my due date actually July 28?
   
   OR
2. If my due date was actually July 27, then wasn't I born 5 days late?
   
   OR
3. If my due date was actually July 27, and I was actually 4 days late, is my birthday really July 31?!
   
   And
4. How is it possible that Monica was a chef in a fancy restaurant, yet she was always home at dinner time?  Shouldn't that be her busiest time of the day and she should be at work?!

I feel so lost :(