I read the post that you lined everything out but still am unsure. My fiancé and I have been sexually active since the end of September. We use condoms every time that we have sex. November 6th was my last really normal period. I have always been regular. Every 26 days. My next one was due on December 1st. I started bleeding the evening of December 1st. It was much lighter flow than I am used to; I still had the cramps, but the blood was more a brownish color. It lasted for five days just like my normal period does. The flow never changed. But I did have to have a tampon because it was enough of a flow. Then on December 16, I started bleeding again. We noticed this after sex. It started brown but by MOnday morning it was it's normal red color. Cramping and passing the small blood clots that I usually have with a normal period. Flow still isn't quite right but it's not like it was at the beginning of the month. I've done a lot of reading. And some places say there is cramping with implantation bleeding, others say there isn't. I took a home pregnancy test yesterday and it was negative. A lot of stresses in my life as of late, increased work load, sudden death in the family, my cat had to have emergency surgery. Have I in fact had my period and it just was irregular. OR should I be concerned about pregnancy? We don't want kids right now but if I am pregnant we will be happy about it.

While no birth control (aside from not having sex) is 100% effective. I highly doubt you are pregnant.

Implantation bleeding is very rare and would be simple spotting, not like the flow of a normal cycle.

As much as us women would like them to be... our periods are not like clockwork. Many many things can effect your cycle. You have admitted to being under a lot of stress... that most certainly could have disturbed your cycle.

Things like change in diet, medication, and stress can cause changes to your cycle. These changes could range from your period being longer or shorter than usual, flow being lighter or heavier, PMS symptoms being different than what you normally get, you could even skip a period altogether.

Again, I think it is highly unlikely you are pregnant. Give it some time for your life to calm down and you should see your periods regulate a bit more.