I have been having these exact same symptoms for about 2 years now, and this blog is the closest thing I have found to an answer. At least I know I'm not crazy!
About 2 years ago I gave birth to my son. When he was about 4 months old I had my first episode of severe leg pain. It starts as a warm tightening high up behind my right thigh and usually within a minute has gotten so bad that I can not walk. At first I thought it was my knee, then maybe my hip. I have had 3 MRIs of my knee, hip and lower back. They found nothing. I have also had countless x-rays. No one has any answers for me, and this debilitating condition hits without notice. Every day I pray that it will not happen while I'm at work or holding my son. I have gone a couple of months in the past without any problems, and then suddenly it will come 3 days in a week. I have found no specific activity or diet that seems to set it off. It usually lasts about an hour, but sometimes can be more like 2. Please, if anyone has any ideas or suggestions, please let me know. Thank you.