I know they are coming out with research that shows that the BCP is not as effective in heavier women (with high BMIs). It gets metabolized more quickly, the hormones aren't enough for the extra weight. That could even be the case for you....since you have more muscle, your metabolism is higher.....muscle is more metabolically active, maybe your body is processing the pill faster???? (I'm talking off the top of my head here...remember I have no medical training...lol)
Regardless, I would talk with your Dr. Explain your cycle, and see what s/he recommends. You might just need a stronger, or weaker, pill.