Impossible to be pregnant right?

Very very unlikely you are pregnant unless you've had unprotected sex since your last period, especially with the 2 negative tests. Your periods could be late cos you are stressing out-stress can affect your cycle, which doesn't help when you are desperately waiting to come on-a viscious circle! It might still be worth a quick trip to the docs though, just to get a check up as they may be able to tell you why you could be late this time. Don't worry about seeming stupid-they are there to help you whether it is a big or small niggle.