18 days late 2 tests and a very excited friend

Me and my partner are trying for a baby. I am now 18 days late and counting. When I was 3 days late I took a pregnancy test... Negative. I thought hmm it could just too early. Did one this morning... Negative. I'm not stressed, just a bit tired. But I've been the same since I started my job in April. I'm not ill (as far as I'm aware). I genuinely don't know how I'm so late as I'm normally like clockwork.

Oh yeah and my friend is really excited about the prospect of a baby. Lol