Hello @samigrace08, like @lioness said, it may be best if you seek medical advice regarding your "pop" sound and pain. I am not a medical professional, but amy quite familiar with internal injuries. A popping sound, followed by quick bruising and swelling is a good indication of some sort of physical injury that may not be wise to ignore. While you weigh your options and whether or not you want to seek medical advice, you may also find this conversation on SI joints of interest, https://connect.mayoclinic.org/discussion/sacroiliac-joint-pain-and-my-introduction/.

@samigrace08, how long ago did you feel the pop and the pain?