What Causes Spotting And Pains After Period With Sudden Weight Gain?

I am 36, I was sterilized in 2000 after the birth of my last child. In 2001 I had cancerous cells removed after an abnormal pap smear. I have not had an abnormal smear test since then. My period finished over a week ago and on Tuesday I had some light brown spotting in my underwear, again and Wednesday and today (Thursday) I'm also experiencing some mild period pains, my breasts are tender and I seem to have gained about 4lbs in weight over the past 2 weeks.