Any advice?

I'm about 6 days late on my period. That had NEVER happened to me. I've taken two test(one was too early, so I took another). The second test wasn't the first urine sample of the day, some test say that matters some do not. Do I test again or go see a doctor? My stomach is upset, I don't want much food and I've been just eating crackers and ginger ale. One of my friends said my body may not produce large amounts of the hormone to be able to see it on the test. Do any of you have any advice it tips for me?! Any help would be great!