Hi. Thanks for your query. Noted the history of severe stomach cramps and bloating wherein you can not stand up straight, laying down makes the pain stop completely, you are a teenager, started period today but never experienced such a pain before. The commonest cause of such a rare thing is an internal hernia; as you stand there is obstruction causing bloating and hence severe pain but on laying down, the pain passes of as the obstructing force is nullified. This can be confirmed by X-ray of the abdomen in standing position when you are in tremendous pain and bloating. Contrast enhanced CT scan can help in getting a correct diagnosis. Diagnostic laparoscopy and sos procedure can help to get a complete relief and tackle any other problem that can be directly visualized.