Bleeding between periods

I am supposed to get my period in 3 days and I have been spotting then bleeding enough for a light or regular tampon for a few days now. it isn't consistent.  This used to happen to me a few months ago where I would bleed going into when I was supposed to get my period and it stopped happening after a few times of this. I went to the gyno she tested for infections and I tested clean so I figured it wasn't caused by anything like that and she said because of my birth control that could be why. I have been on the same one for almost two years and it is a low dosage. Is it because I have been taking it at about a 1-2 hour difference the last few weeks everyday? Do I need to start a higher dosage?