Late period

Hi, I was hoping to get some advice. My cycle length has always been 28 days and is very rarely late. I had unprotected sex on day 19 (5 after my ovulation, 4 after the end of my window). I'm currently 2 days late and have gotten 2 negative tests. I was recently very sick with the flu and still have a cough and occasionally vomit so I don't know if I'm having any symptoms or not. I plan to wait a few more days before taking any more test but was wondering how soon symptoms can start and when I would get a postive if I am actually pregnant. Thank you for any advice and help.