I'm currently visiting a physio for problems that seem rather similar - he says it's down to a number of things, one of which is a lack of core stability, and has me doing lots of Pilates style stuff (IMO very similar to yoga).
Wouldn't like to give any specific advice - the cause of your problem may be completely different to mine. Has your problem been diagnosed by anyone, and if so, did they not advise what to do about it?
I also have a problem with my left glute, so my hamstring is doing more work, leading to something that feels very much like sciatica.
Any particular yoga moves that you find have helped you?