Is It Common To Miss A Period When Switching From

Is it common to miss a period when switching from the depo shot to the pill? My last depo was November, I recently went on the pill. My first period was due Sunday, still nothing as of today. I took a pregnancy test Sunday, but it was negative. Please help, is there a chance I could be pregnant? I went on the pill to regulate my cycles because we want to try and conceive within the next 6 months or so, thinking it wasn't possible to try right now.