strong positives 4 days before AF?

Isla
Hi All, 
Just wondering if anyone had anything similar? I took two tests 4 days before AF was due and am so over the moon that they both came back positive. The line was so dark and so quick when I took the first test, do you think I may have got my dates wrong or maybe just lots of hormones flying around? I calculate that I should have been 3 weeks 4 days when taking these tests. 
Thanks for your help, you lovely bunch 
Xx