Re: in pain & confused?
I'm assuming that when you said "yesterday", you were saying that the day that you wrote this post, you didn't have that pain any longer?
It's hard to say what could have caused it based on this bit of information. It could be almost anything from menstrual to bowel to lower back injury.
The fact that you've likely gotten past it, means that it's not likely to be anything of any concern. However, if it reoccurs, the only one who can tell you what may or may not be going on is your doc. I'd speak to him/her if you continue getting it and there's no relief.