If you have been regular with your pill intake, you are amply protected. This irregular spotting could be due to hormone imbalance
. Such things often happen while on the pill, but, usually in the initial months. Please get a proper clinical evaluation and if necessary, a blood test
and complete hormone profile. A trans-vaginal sonogram can help to exclude ovarian causes. Local lesions like vaginitis
, erosions, polyps and sudden weight changes along with stress also can cause such spotting. Hope this helps.