On May 18,2013 I past blood like I was starting my cycle but the next day I wasn't bleedin anymore and I like to know why it did that?

No way to know. It could be that you were having an off month, it could be break through bleeding, it could be a miscarriage (if you're sexually active), it could be that you're pregnant, it could be cancer, there are so many options.

If this is a concern you should see your doctor, he/she is the only one that can do an exam and tell you what's going on. That's impossible to do online, and you won't find any answers on the internet, only possibilities.

Good luck.