any ideas?

Bobbi • Ukulelelove
I told my mom last night I was 3 days late on my period.. 
something that's hard for me to do cause I'm usually quiet and google everything that happens to my body. 
(Not a safe thing to do) 
Anywhoo
I went to sleep and was woken up by my big sister (who is pregnant) and she gave me a pregnancy test, because my mom thinks I'm a idiot. 
I was 3 days late. 4 days now and the test was a negative. 
I'm glad it was
I'm only 19 
But do you think it was to early to have taken it? 
When me and my boyfriend has sex, it was protected but I'm a very paranoid person, and maybe the feeling of stress is causing it to be late? 
Or maybe it's cause of my thyroid?