Like Sunworshiper said, the length of time on them won't matter. This is because they're hormonal and disrupt the natural cycle of the female body and some just take time to readjust thenselves.
It doesn't matter how long you were on the pill what Clysta said is correct
What if I had only been on the pill for a month and a half?
Retest with first morning urine and limit what you drink. Testing late in the day, especially after drinking so much will cause inaccurate answers. It's also possible your body is still adjusting to being off of birth control. Some women can take months and others take no time at all.
I had the same problem only I skipped my period for three months Qhen I came off of my birth control. Your body could just brrr adjusting the cycle and it is normal to miss a few months but if you miss more than 3 I would suggest to call your dr.