Help with late periods???

Okay..I don’t get it..I have never been late on my period..my first daughter, right after I had her my periods were back to normal. My second daughter was born in July..I got my period shortly after the month after that i was 5 days late and it was about 3 days which is pretty short for me..than this month I am 3 days late at the moment and negative test...maybe my body is still trying to get back to normal, but it is also freaking me out!!!