chances of being pregnant while on birth control?

My hubby and I are not even ttc. I am on the patch but have they have fallen off here and there before. Anyway, I have started lite bleeding about 1.5-2 weeks before my period usually starts. It is not the typical flow of my period and looks different (somewhat resembles the implantation bleeding I keep reading about) and is very light (only bleeding when I wipe). And I am somewhat nausous, a little lower back pain, very dizzy, headaches 3 out of the last 5 days, more acne on my chest, shoulders and face, and extremely exhausted. If I had not been on bcp I would def. think I was pregnant, but since i have been on bcp I wonder if I am just imagining things. It is too early to test unfortunately...anyone else have a similar situation?