My cycle is 30 days late? HELP.

Hey, guys. So my cycle is 30 days late. Up until the beginning of last year, my cycles weren't really regular. They weren't ever this off, but they weren't regular either. But for the past year or so they've been pretty regular. But now all of a sudden I've missed it by 30 days today. I took a pregnancy test last week, but it was negative. The test was about 5 months old, but wasn't expired based on the expiration date on the side of the box. I don't really have any other signs of pregnancy. I don't know what to do.