13 day late period- what is going on?

I am 31. 13 days late period. Although today I have a lil bloody mucus when I wipe. Have felt tired last 3 days. Light headed. Even some slight nausea. Non of these symptoms are normal for me. My husband had a vasectomy 9 years ago. I took 1 HPT it was negative but with my other 2 kids they showed up negative til further along. Have also lost 3 pounds in 2 days without trying. What are some reasons for feeling this way?