bleeding while on a continuous cycle

I've been continuous cycling on chateal birth control since August with the occasional break through. All of my breakthroughs happen right after I have sex... some of it is spotting, and then other times it turns into a very heavy miserable period for a few days. My breasts have been very tender off and on since I started the new method, I noticed my nipples were slightly discolored a week ago and that freaked me out. I had sex yesterday and am now experiencing the heavy breakthrough bleeding. Is the breakthrough that I'm experiencing when I have sex normal? Or cause for concern? What would anyone recommend doing when the breakthrough happens, I was told to keep taking the pills as normal and it will stop (which it does) also, should I be concerned about my breasts being as sore as they are? Any help or input would be greatly appreciated!