I dont think it is your body adjusting to the pill. Ortho - Lo is a very low dose pill and there have been many many women come to this forum complain about what you are complaining about. You are having breakthrough bleeding because the hormones in your pill are not enough. You SHOULD be protected against pregnancy, but if it were me, I wouldn't rely on ortho-lo, I would switch to a regular dose like Tricyclen.
i had breakthrough bleeding two times in the last year. i wouldn't worry. if you are concerned, you can always take a visit to the doc.