late period help

[Adeno2020]

hi. While my periods are never bang on I’m always either every 3 weeks or every 4 weeks. For example I had one 25th March. Which was 4 weeks from previous then I had one 3 weeks later at 15th April. So technically I should of weighed been on last Saturday (3 weeks) or yesterday being 4 weeks. But I’m still not on. I’m never usually late last 4 weeks normally before 4 weeks it’s even been every 2 weeks before ? I’ve had head aches and I was sick last night with a really bad head out it down to a migraine