What's Going On

my period is late and I am never late I always on time or early I have done pregnancy test and there all negative if I was pregnant I would be 3 weeks and 6days today is it to early to come up all my other 3 children I have tested at 6+weeks and they were faint line positive am I to early to tell I have been nausea and tired all the time and my body feels different I had spotting which wasnt anything like a period doctor said implantation bleeding or something how long should I wait to test again and I tested this morning negative again please help me ladies