Pregnant or Overthinking?

So I've had a mirena IUD for a little over 5 months now and my periods were starting to regulate, this most recent period hasn't come yet, I'm 4 days late and stressing, the last time I had unprotected sex was 3 weeks ago and I feel normal but no period, I have (TMI) thick milky white colored discharge but nothing else and I said I wasn't gonna worry about it but I am, some people say they stopped getting their period after a year, some say a couple months. Another person said it might be because I'm stressed as I am graduating high school soon. Should I be worried? What should I do?