Period 21 days late and every test is negative

My period have been irregular ever since having my son a year ago. It changes from 28 days to some then being 31 day cycles. Never more or less. So my period is either 21 days late(June 5th)or 15 days late(June 11th)The last time I had my period was may 8th. I’ve tested four times, I’m waiting four to three days between and all negative, not even a faint line.

I’ve had cramping like I’m going to get my period but still nothing.

With my son I tested positive right away, maybe four days after my missed period.

So I guess I’m wondering is there any ladies who have had the same experience and been pregnant or was it something else? It’s starting to worry me.

Update: period just started 31 days late.