I Have Been In Menopause For About 4 Years. I

I have been in menopause for about 4 years. I had a pap smear December 11, 2015, which is normal. On December 16th I was snow shoveling, which I took three 15 minute breaks. I was stomach started cramping and my back. On December 17th I started bleeding slightly, which I had to start wearing pads. My stomach has been cramping since and I have been bleeding slightly off and on. What has caused this?