Could I be pregnant

Ok so how to explain this... my son is 11 months old I am 26.... prior to my son my cycle would go anywhere from 51-62 days and period would last all of 2-3. After my son was born, my period lasted 2 days, and then my cycle has been a consistent 28-30 days with a period lasting of about 3-4 days....

Well now I am on day 51, and still no period... I have been quite nauseated, and I have taken 3 pregnancy tests, one didn't read and two both came up negative....

Am I possibly pregnant and it's too early to tell? Or is my period just rotating back to how it used to be prior to having my son?

Thanks for all advice in advance