R.L.
It is normal to be a little irregular until your body adjusts to the hormone changes. You may not have your period every 28 days, you may go longer or shorter between periods. You may have some spotting in between periods too. I also became pregnant within a few months of stopping the pill, but since you took the pg tests you are most likely not pregnant. I would suggest to keep being careful and wait and see. Of course if you are concerned give your OB's office a call and talk to the nurse. They are very helpful with questions like this!