Periods after stopping the injection

I started the depo injection in march '19, my last depo injection was October'19 - I was due my next injection December 13th and I never went for it.

My periods practically stopped within a month of starting the depo. However since stopping the depo my periods seem yet to regulate, they appeared to return in may'20 (8months after last injection) and they regulated and my last period was in august which came exactly a month following the previous period.

HOWEVER i am now 30 days late for my period! I keep taking tests to rule out pregnancy and its always negative.

In recent weeks I wake up with horrible heartburn and slightly nauseous, but still tests are coming back negative.

Advice please 😭