My period was from 11/9 to 11/11, but it was suppose to start 11/5. I've been on BC since May but just switched to Yaz in October. I haven't been taking them at the same time everyday and I've had to take 2 or 3 pills every time to make up the missed pills. I had unprotected sex on 11/19 and twice on 11/21. On Sunday, 11/23, I started to feel different. I felt like I had a mild case of the cramps and I felt like something was different in my lower region. I'm not due for my next period until 12/3. My boobs started to feel tender and hurt when water hit them in the shower. I've been cramping on and off for the last 5 days and I've had a mild case of diarrhea for the last few days as well. I've had headaches and lower back pain as well as slight nausea for the last couple days. Yesterday, I started what I think is my period, but it's a week early and it is different than normal. It isn't spotting, but it isn't extremely heavy either. It started as a really dark brown and now it is a mixture of dark brown and dark red and There was a very large clot in my pad today. I'm very regular and never start a week early. I cramped really badly right before it started, but it disappeared once it started. Could I be pregnant and could the bleeding be implantation bleeding?

Yes you could be pregnant, no form of birth control is 100% effective, especially if you don't take it as prescribed.

It could be that your period came early because you keep missing pills. This will throw your body out of wack. It's very important to take your pills daily and try to take them around the same time every day.

Also, double up on birth control, if you want to lower the risks of pregnancy. A good combo is the pill and a condom, but even then you aren't 100% protected against pregnancy.

The only guarantee to prevent pregnancy is abstinence.

Good luck.