have a question...

Megan
So I'm in need of some help/insight. I had my son in January of this year and of course I bled for a while afterward (2weeks) and I had 1 period since and now my period is 21 days late also I've took two pregnancy tests and it was negative at first but after they sat a while the other line showed up positive....? Should I be worried or is this sort of thing normal..?