Is Weight loss and bleeding a sign of pregnancy?

Here is my senerio:
I am 28 years old, married and I have 3 children: 4 yrs old and a set of 10 month old twins. I am currently taking birth control (tri-cyclen-LO). I am due to have my period next week. I have been trying to lose the baby weight from my last pregnancy and and have been stuck in a lul for about 5-6 weeks...Untill last week. I lost 6 lbs in one week without really doing anything different. Two days ago I went out for a brisk walk and when I came back I noticed a pink spot on my underwear. During that day I had a couple of light pinkish/brownish bloody spots and clots. The next day there was none and today it is back. I am nervous that I may be pregnant as we weren't trying and didn't really expect to have any more children. It this a possible sign of pregnancy or maybe related to something else?