cold and tired

I've been feeling really cold for a week. I was supposed to get my period today, but nothing yet. I have a very regular 28-day cycle and have never used the pill or anything like that. Today I was doing some chores with my husband and had really bad pain in my uterus. Then I got a few drops of blood and nothing the rest of the day. It seemed like it was coming through the cervix, because it hurt.