I have the similar problem. It caused by the discs in the sacrum. sometimes the pain goes all the way down to my right foot. Also I have a degeneration arthritis in my pelvis. The doctor just told me today that it was caused by over use this area. I think I might did too much hip opening in yoga practise. And the natural path told me that I need to find the balance between yoga practise and health. Sweating crazy everyday will gradually damage my body. Now I already have skin disorder. he believes it caused by heat.